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UNIVERSITY  OF  CALIFORNIA. 

Class 


EXERCISES  IN  ELEMENTARY  QUANTITATIVE 
CHEMICAL  ANALYSIS 


THE  MACMILLAN  COMPANY 

NEW  YORK  •    BOSTON  •   CHICAGO 
ATLANTA  •   SAN   FRANCISCO 

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LONDON  •    BOMBAY  •    CALCUTTA 
,     MELBOURNE 

THE  MACMILLAN  CO.  OF  CANADA,  LTD. 

TORONTO 


EXERCISES 


IN 


ELEMENTARY  QUANTITATIVE 
I       CHEMICAL  ANALYSIS 

FOR  STUDENTS  OF  AGRICULTURE 


BY 
AZARIAH    THOMAS    LINCOLN,    PH.D. 

ASSISTANT  PROFESSOR   OF  CHEMISTRY,   UNIVERSITY 
OF  ILLINOIS 

AND 

JAMES   HENRI    WALTON,   JR.,   PH.D. 

ASSISTANT  PROFESSOR   OF  CHEMISTRY,   UNIVERSITY 
OF  WISCONSIN 


Nefo  fforfc 
THE    MACMILLAN   COMPANY 

1907 

All  rights  reserved 


v 


COPYRIGHT,  1907, 


Set  up  and  electrotyped.     Published  December,  1907. 


NortoooU 

J.  8.  Cashing  Co.  —  Berwick  &  Smith  Co. 
Norwood,  Mass.,  U.S.A. 


PREFACE 

OWING  to  the  growing  demand  for  quantitative  analytical  chem- 
istry by  those  engaged  in  the  study  of  agriculture,  it  seemed  to 
the  authors  that  the  presentation  of  the  fundamental  methods  of 
agricultural  analysis  as  carried  out  in  the  laboratories  of  the 
American  Experiment  Stations  would  be  desirable.  While  this 
book  is  designed  primarily  as  an  elementary  quantitative  guide 
for  the  use  of  agricultural  students,  it  may  also  be  used  for  the 
work  in  general  elementary  quantitative  analysis. 

This  text-book  is  the  outgrowth  of  several  years'  experience  in 
teaching  quantitative  analysis  to  students  specializing  in  Agri- 
culture, Chemistry,  Medicine,  and  Household  Science.  No  attempt 
has  been  made  to  present  a  complete  treatise  on  quantitative 
analysis ;  but  a  few  typical  exercises  have  been  chosen  to  illustrate 
the  fundamental  principles  and  the  most  important  methods  of 
manipulation.  To  further  the  interest  in  this  work,  the  student 
should  be  encouraged  to  do  considerable  outside  reading,  and 
there  should  be  available  for  his  use  a  number  of  the  best  books 
of  reference.  In  the  Appendix  will  be  found  a  list  of  some  of  the 
most  important  works  having  a  bearing  on  this  subject,  while 
throughout  the  text  reference  is  made  to  the  original  literature. 

The  gravimetric  exercises  and  the  work  outlined  under  Acidime- 
try  and  Alkalimetry,  together  with  the  analysis  of  Milk  or  Feeding 
Material  and  Fertilizer,  comprise  the  work  usually  accomplished 
by  the  agricultural  students  in  one  semester.  Those  students  who 
desire  more  quantitative  analysis  complete  the  remainder  of  the 
exercises  in  another  semester. 

Owing  to  the  importance  of  the  calculation  of  analytical  data, 
this  subject  has  been  treated  in  considerable  detail  in  Part  V 
(Stoichiometry).  The  matter  presented  is  arranged  to  be  studied 
in  conjunction  with  the  regular  laboratory  exercises.  In  addition 
to  the  methods  of  solving  problems,  a  large  number  of  problems 
is  given  for  practice.  The  selection  has  been  made  with  the  idea 
of  emphasizing  the  fundamental  principles  brought  out  in  the 


174976 


vi  PREFACE 

laboratory  exercises,  and  many  of  the  problems  are  taken  from 
the  experimental  data  of  the  students. 

Although  it  will  be  found  convenient  to  have  a  certain  amount 
of  platinum  ware  available  for  these  exercises,  it  is  not  necessary. 
Porcelain  crucibles  and  dishes  may  be  used  for  all  the  determina- 
tions, with  the  possible  exception  of  the  alkalies  in  soils. 

The  notes  which  are  introduced  throughout  the  text  emphasize 
the  important  points  and  may  serve  as  the  basis  of  the  classroom 
work,  which  should  be  an  important  feature  of  instruction  in  quan- 
titative analysis. 

In  preparing  this  manual,  free  use  has  been  made  of  the  various 
standard  works  on  quantitative  analysis,  of  the  publications  of  the 
Association  of  Official  Agricultural  Chemists,  of  the  Bulletins  of 
the  United  States  Department  of  Agriculture,  Bureau  of  Chem- 
istry, and,  particularly,  of  Leach's  excellent  treatise  on  Food 
Inspection  and  Analysis. 

The  authors  desire  to  express  their  gratitude  to  Mr.  J.  H.  Pettit, 
Assistant  Professor  of  Soil  Fertility,  University  of  Illinois,  for 
many  valuable  suggestions  on  the  determinations  connected  with 
Fertilizers  and  Soils ;  to  Mr.  Cyril  G.  Hopkins,  Professor  of 
Agronomy,  for  his  help  in  correcting  the  proofs  of  the  Analysis 
of  Fertilizers  and  of  Soils  ;  and  to  Mr.  D.  L.  Weatherhead,  for 
assisting  in  solving  the  problems. 

A.  T.  L. 
J.   H.  W.,  JR. 
URBANA,  ILLINOIS,  August  i,  1907. 


CONTENTS 

PART   I 
INTRODUCTION 

PAGE 

GENERAL  REMARKS i 

NOTEBOOKS   2 

REAGENTS 4 

SPECIAL  APPARATUS 5 

Desiccators 5 

Wash  Bottles 6 

Stirring  Rods 6 

OPERATIONS  OF  QUANTITATIVE  ANALYSIS 6 

Sampling 6 

The  Weighing  of  Samples 7 

Solution  and  Evaporation 8 

Precipitation        .         .         .         .         .         .         .         .         .         .         .10 

Conditions    .         .         .         .  .         .         .         .         .         .10 

Enlargement  of  the  Grains  of  Crystalline  Precipitates    .         .         .11 

Colloidal  Precipitates 12 

Filtration 12 

Washing 13 

The  Drying  and  Ignition  of  Precipitates 14 

Crucibles      ............       14 

The  Use  and  Care  of  Platinum    .         .         .         .         .         .         .         .15 

THE  BALANCE 16 

The  Construction  of  the  Balance 17 

Position  of  Center  of  Gravity       .         .         .         .         .         .         .         .17 

Knife-edges 18 

Beam 18 

The  Weights 19 

Summary  of  Precautions  to  be  observed  in  Weighing    ....  20 

PART   II 

GRAVIMETRIC  ANALYSIS 

EXERCISES  WITH  THE  BALANCE 22 

EXERCISE  I  —  Determination  of  the  Time  of  Vibration  22 


viii  CONTENTS 

PAGE 

EXERCISE  II  —  Determination  of  the  Zero  Point 22 

EXERCISE  III  —  Determination  of  the  Sensitiveness     ....  23 

EXERCISE  IV  — Weighing  by  the  Usual  Method          ....  23 

GRAVIMETRIC  DETERMINATIONS 24 

EXERCISE  V  —  The  Determination  of  Chlorine 24 

EXERCISE  VI  —  The  Determination  of  Sulphur  in  a  Soluble  Sulphate  .  29 
EXERCISE  VII  —  Separation  and  Determination  of  Calcium  and  Mag- 
nesium in  a  Mixture  of  their  Carbonates    ......  32 

EXERCISE  VIII  —  The  Determination  of  Aluminium  in  a  Soluble  Salt  .  37 


PART   III 

VOLUMETRIC  ANALYSIS 

GENERAL  DISCUSSION 40 

Volumetric  Apparatus 40 

Pipettes 40 

Cylinders 41 

Flasks 41 

Burettes         .         .         .         .         . 42 

Calibration  of  Graduated  Apparatus 43 

EXERCISE  IX  —  The  Calibration  of  a  Burette        ....  45 

Standard  and  Normal  Solutions          .......  49 

ACIDIMETRY   AND   ALKALIMETRY 5! 

General 51 

Indicators    .         .  .........  52 

Litmus  ...........  52 

Phenolphthalein    .         .         .         .         .         .         .         .         .         .52 

Methyl  Orange      ..........  52 

Cochineal 52 

Notebooks    ............  53 

THE  PREPARATION  OF  STANDARD  AND  NORMAL  SOLUTIONS  .        .        -54 

Methods  of  Standardization         .......         .         .         .         .  54 

a.  By  Precipitation       .         .         .         .  .         .         .         -54 

b.  By  Titration    .         .         .         .       .,-",.-.         .         .  54 

c.  By  the  Absorption  Method       .         .        *        .         .         .         -55 

EXERCISE  X  —  Preparation  of  an  Approximately  Half-Normal 

Hydrochloric  Acid  Solution  .  .  .  .  .  .  55 

EXERCISE  XI  —  Preparation  of  an  Approximately  Half-Normal 

Potassium  Hydroxide  Solution  .  .-..,...  ,.  .  ..  .  56 

EXERCISE  XII  —  The  Titration  of  the  Acid  against  the  Alkali       .  56 


CONTENTS  ix 

PAGE 

STANDARDIZATION  OF  THESE  SOLUTIONS •     .  57 

EXERCISE  XIII  —  Standardization  of  the  Hydrochloric  Acid  Solu- 
tion    57 

a.  By  Precipitation  of  the  Chlorine  as  Silver  Chloride   .         .  57 

b.  Against  Calcium  Carbonate       ......  59 

EXERCISE  XIV  —  Standardization  of  the  Alkali  Solution       .         .  59 

a.  Against  Pure  Chemicals -59 

b.  By  the  Absorption  Method 60 

EXERCISE  XV  —  Determination  of  the  Percentage   Strength   of 

Acid  Solutions  ..........  62 

EXERCISE  XVI  —  The  Analysis  of  a  Soluble  Carbonate  .  .  63 
EXERCISE  XVII  —  The  Determination  of  Total  and  Caustic  Alkali 

in  a  Mixture  of  Sodium  Hydroxide  and  Sodium  Carbonate         .  63 

OXIDATION  AND  REDUCTION 64 

General .         .         .64 

Available  Oxygen 65 

The  Permanganate  Method 67 

EXERCISE  XVIII  —  Preparation  of  a  Solution  of  Potassium  Per- 
manganate        .         .         .  .         .         .         .         .         .67 

EXERCISE  XIX  —  Standardization   of  a   Solution    of   Potassium 

Permanganate    ..........  68 

a.  By  Pure  Iron  dissolved  out  of  Contact  with  the  Air  .         .  68 

b.  By  Pure  Iron  reduced  by  Means  of  the  Jones  Reductor      .  69 

Determination  of  the  Blank 70 

Reduction  and  Titration  of  the  Iron         ....  71 

c.  By  Ferrous  Ammonium  Sulphate        .         .         .         .  71 

d.  By  Means  of  Sodium  Oxalate    .         .         .         .         .         .72 

EXERCISE  XX  —  The  Determination  of  the  Percentage  Purity  of 

Oxalates 72 

EXERCISE  XXI — The  Determination  of  the  Purity  of  Hydrogen 

Peroxide 73 

EXERCISE  XXII — The  Determination  of  Calcium  73 

EXERCISE  XXIII  —  The  Determination  of  Iron  in  Siderite    .         .  74 

The  Dichromate  Method       .         .         .         .         .         .         .         .         -75 

Preparation  of  a  Solution  of  Potassium  Dichromate  ...  76 

Indicator 76 

EXERCISE  XXIV  —  Standardization  of  a  Solution  of  Potassium 

Dichromate 76 

a.  Against  Ferrous  Ammonium  Sulphate        ....  76 

b.  Against  Pure  Iron      .         .         .         .         .         .  77 

EXERCISE  XXV  —  The  Determination  of  Iron  in  Siderite      .         .  77 

lODIMETRY 78 

Methods  of  Determination    .         . 78 

a.  The  Titration  of  Oxidizable  Bodies 78 

b.  Bodies  which  contain  Available  Oxygen  78 


CONTENTS 


c.   Free  Chlorine  or  Bodies  which  liberate  Chlorine       ...  78 

EXERCISE  XXVI — Preparation  of  Solutions          ....  79 

a.  Approximately  N/io  Iodine  Solution         .         .  .79 

b.  N/io  Sodium  Thiosulphate  Solution          ....  79 

c.  Starch  Solution 80 

EXERCISE  XXVII  —  Standardization  of  the  Iodine  Solution          .  So 

a.  Against  N/io  Thiosulphate 80 

b.  Against  N/io  Arsenious  Oxide 80 

c.  By  Means  of  Standard  Permanganate  Solution  .         .         ..  81 

d.  By  Means  of  Standard  Dichromate  Solution       ...  82 
EXERCISE  XXVIII  — Estimation  of  Available  Chlorine  in  Bleach- 
ing Powder 82 

EXERCISE  XXIX  —  The  Determination  of  Available  Oxygen  in 

Pyrolusite 83 

EXERCISE  XXX  —  The  Determination  of  the  Strength  of  Hydro- 
gen Peroxide 84 


PART    IV 
AGRICULTURAL   ANALYSIS 

THE  ANALYSIS  OF  MILK 85 

General       .         .         .         . 85 

Composition          .         .         .         .         .         .         .         .         .         .         -85 

Sampling     ............       86 

Specific  Gravity  .         .         .         .         .         .         .         .         .         .         .86 

Removal  of  Samples    .         .         .         .         .         .         .         .         .         .87 

Total  Solids 87 

Ash 88 

Fat 88 

a.  Adams'  Paper  Coil  Method 88 

b.  Babcock  Method 90 

Total  Proteids      ...........       94 

Kjeldahl  Method 94 

Determination  of  the  Blank 97 

Milk  Sugar 99 

Tabulation  of  Results .100 

References   .         .         .         .         .         .         .         .         .         .         .         .100 

THE  ANALYSIS  OF  BUTTER 100 

General 100 

Sampling 101 

Water 101 

Fat 102 

Casein         .        .        . .  102 

Ash 102 

Salt  102 


CONTENTS  xi 

PAGE 

THE  EXAMINATION  OF  BUTTER  FAT 103 

Composition 103 

Differences 105 

Chemical 105 

Physical 105 

Preparation  of  Pure  Butter  Fat 105 

Physical  Tests 106 

Specific  Gravity      .         .         .         .         .         .         .         .         .106 

Melting  Point 107 

Chemical  Tests      .         .         .         .         .         .         .         .         .         .109 

Volatile  Fatty  Acids no 

Reichert-Meissl  Method  .         .         .         .         .         .  110 

Soluble  and  Insoluble  Fatty  Acids 112 

Saponification  or  Koettstorfer  Number 114 

Iodine  Absorption  Number,  Hanus  Method    .         .         .         .116 

Household  Tests 118 

The  Foam  Test 118 

Waterhouse  or  Milk  Test 118 

References     .         .         .         .         .         .         .         .         .         .         .119 

THE  ANALYSIS  OF  CEREALS  AND  FEEDING  MATERIALS  .        .        .        .119 

Classification 119 

Composition          .         .         .         .         .         .         .         .         .         .         .119 

Carbohydrates 120 

Fats 121 

Proteids 121 

Preparation  of  the  Sample 121 

Dry  Matter 121 

Ether  Extract 123 

Separation  of  Carbohydrates,  Stone^s  Method       .         .         .         .         .123 

Reducing  Sugars,  Allihn's  Method 124 

Sucrose.  Clergefs  Inversion  Method 124 

Dextrin  and  Soluble  Starch 125 

Starch,  Diastase  Method 126 

Starch,  Saliva  Method 127 

Crude  Fiber 128 

Total  Proteids 129 

Ash 129 

References 130 

THE  ANALYSIS  OF  FERTILIZERS 130 

General 130 

Sampling 131 

Dry  Matter 132 

Phosphorus 132 

Total  Phosphorus 133 

Water-soluble  Phosphorus 136 


xii  CONTENTS 

PAGE 

Citrate-insoluble  Phosphorus         ...        .        .        .         .136 

Citrate-soluble  Phosphorus  .  . 137 

Nitrogen I38 

Total  Nitrogen  in  Absence  of  Nitrates 138 

Total  Nitrogen  when  Nitrates  are  Present  .  .  .  .  .138 

Nitrogen  Soluble  in  Water  .  - 139 

Nitrogen  as  Ammonium  Salts .  140 

Potassium  ...  . j^o 

Potassium  in  Mixed  Fertilizers 1-40 

References   .        .        .        .        .  , I42 

THE  ANALYSIS  OF  SOIL, 142 

Constituents  of  the  Soil 142 

Organic  Constituents 143 

Collection  and  Preparation  of  the  Samples   .         .         .         .         .         .144 

Moisture 146 

Volatile  Matter 147 

The  Extraction  of  the  Acid-soluble  Material         .         .         .         ...     147 

Removal  of  Soluble  Silica  from  Solution 148 

Insoluble  Matter  and  Soluble  Silica 149 

The  Determination  of  the  Acid-soluble  Substances          .         .        .         .150 
Iron,  Aluminium,  and  Phosphorus,  collectively       .         .         .         .150 

Phosphorus 151 

Manganese    .         . 151 

Calcium 152 

Magnesium   .         .         .'•"...         .         .         .         .         .         .         .152 

Sulphur         .         .         .  •       .         .         .         .         .         .         .         .152 

Iron 153 

Potassium     .         .         .         .         .         .         .         .         .         .  153 

Sodium          .         .         .         .         .         .         .         .         .         .         .     153 

Separation  of  Potassium  from  Sodium 153 

ffumus        .         .         .         .         .         .         .         .         .         .         .         .154 

Total  Nitrogen  in  the  Presence  of  not  More  than  a  Trace  of  Nitrates    .     155 
Carbon  Dioxide    .         .         .         .         .         .        .         .         .         .         .156 

Statement  of  Results .         .        .         .     159 

References   .        .         .        .         .         .         .  .         .         .         .     160 


PART   V 

STOICHIOMETRY 

EMPIRICAL  FORMULAS  .  -.  -.  .  -.  -.  .  .  .  ~  .  161 

Problems  '  .  .  .  .  .  ;  .  ;  .  .  .  .162 

PERCENTAGE  COMPOSITION  .  .  -.  >  .-  >.  .  •  ..y  •  162 

Problems  ,  '  „  .  ,  •  .-  ...  ..,..'...•  *  ..  .''  .  163 


CONTENTS  xiii 

PAGE 

GRAVIMETRIC  CALCULATIONS    .        .        .        .        .        .        .        .        .163 

Factors 165 

Problems  .  .  . 166 

Indirect  Methods .167 

Problems .  .  .  168 

The  Volume  of  a  Reagent  Necessary  for  a  Given  Reaction  .  .  .169 

Problems .  -     171 

VOLUMETRIC  CALCULATIONS     .  .  ....     171 

Acidimetry  and  Alkalimetry I71 

Problems /    .         -^     .         •     i?7 

Oxidation  and  Reduction      .         .         .         .         •  ^  .178 

Balancing  Equations 178 

Oxidizing  Agents .         .         .         .         .         •         •         •         •         .180 
Exercise  in  Balancing  Equations  .         .         .         .         .         .         .181 

PERMANGANATE  AND  BICHROMATE  METHODS 182 

Numerical  Relations     .         .         .         .         .         .         .         •         •         .182 

Questions  on  Equations        .         .  ,^ 183 

Methods  of  Solving  Problems       .  ...  .184 

Problems .  .186 

lODIMETRY 187 

Method  of  Solving  Problems        . 187 

Questions  on  Equations 188 

Problems 188 

FACTOR  WEIGHTS 189 

Miscellaneous  Problems 190 


APPENDIX 


BOOKS  OF  REFERENCE      

195 

TABLE         I. 

Desk  Reagents    

196 

TABLE       II. 

Laboratory  Reagents  

196 

TABLE      III. 

Apparatus  for  Desk  Equipment  

202 

TABLE      IV. 

Specific   Gravity  of  Hydrochloric,    Nitric,   and   Sulphuric 

Acids      

203 

TABLE       V. 

Specific  Gravity  of  Ammonia  Solutions        .... 

205 

TABLE      VI. 

Determination  of  Lactose  by  Soxhlefs  Method    . 

206 

TABLE    VII. 

Determination  of  Dextrose  by  Allihn's  Method    . 

207 

TABLE  VIII. 

Logarithms          ......... 

210 

TABLE      IX. 

Antilogarithms    

212 

TABLE       X. 

Combining  and  Atomic  Weights          ..... 

214 

ANSWERS  TO 

PROBLEMS    

2I5 

INDEX 

217 

LIST   OF   ILLUSTRATIONS 

FIG.  PACK 

1 .  Sample  Pages  of  Notebook  .         .         .         .         .         .         .         .         .  3 

2.  Desiccator 5 

3.  Wash  Bottle 6 

4.  Cover-glasses  and  Clip 8 

5 .  Triangle  for  supporting  Cover-glasses 9 

6.  Evaporation  of  Liquid  from  a  Crucible          ......  27 

7.  Ignition  of  Precipitates 30 

8.  Half-form  Filter 37 

9.  Pipettes 41 

10.  Graduated  Cylinder 41 

1 1 .  Graduated  Flask 42 

12.  Burettes  and  Holder 42 

13.  Reading  Burettes          ..........  43 

14.  Calibration  Curves        ..........  48 

15.  Recording  Volumetric  Data          . 53 

1 6.  Gooch  Apparatus 58 

17.  Absorption  Flask 61 

18.  Dissolving  Iron  out  of  Contact  with  Air 69 

19.  Jones  Reductor    ...........  70 

20.  Apparatus  for  Determination  of  Available  Oxygen        ...  83 

21.  Muffle  Furnace    ...........  89 

22.  Extraction  Apparatus  .         .         .         .         .         .         .         .         .         .  90 

23.  Extraction  Battery,  heated  Electrically 91 

24.  Ether  Distilling  Apparatus 92 

25.  Centrifugal  Machine 93 

26.  Digestion  and  Oxidation  Battery 95 

27.  Apparatus  for  Distilling  Ammonia  in  Kjeldahl  Determination      .         .  96 

28.  Specific  Gravity  Flask 106 

29.  Weighing  Tube  for  Butter 109 

30.  Reflux  Hopkins  Condenser  and  Flask 125 

31.  Copper  Distilling  Flask 156 

32.  Apparatus  for  Determination  of  Carbon  Dioxide 157 


xv 


OF  THE 

f    UNIVERSITY   ) 


PART    I 

INTRODUCTION 

GENERAL  REMARKS 

THE  knowledge  of  the  amount  of.  a  particular  constituent  in  a 
substance  is  often  of  great  importance  from  the  commercial  as  well 
as  from  the  scientific  standpoint.  The  necessity  of  being  able  to 
answer  the  question  "  How  much  ?"  with  a  high  degree  of  accuracy 
has  led  to  the  development  of  the  important  branch  of  chemistry 
known  as  Quantitative  Analysis. 

The  methods  of  quantitative  analysis  may  be  classified  according 
to  the  nature  of  the  operations  employed.  The  most  important 
are  the  following : 

~  ,       [Gravimetric 

General 

T\/T  *.u  j       i  Volumetric 
Methods 

[Electrolytic 


Special 
Methods 


Gasometric 
Colorimetric 
Photometric 
Attributive 


In  the  following  pages  the  gravimetric  and  volumetric  methods 
only  will  be  discussed.  For  a  description  of  the  other  methods  the 
student  is  referred  to  the  more  comprehensive  works  on  quantita- 
tive analysis,  a  list  of  which  is  given  on  page  195. 

In  gravimetric  methods  the  constituent  is  determined  by  trans- 
forming it  into  an  insoluble  compound,  in  which  condition  it  can  be 
separated  by  filtration  from  the  other  constituents  which  were  orig- 
inally present  in  the  substance.  This  insoluble  compound  either 
has  a  definite  chemical  composition  or  it  may  be  changed  into  a  sub- 
stance of  known  composition.  It  is  weighed  and  the  amount  of 
the  constituent  sought  calculated. 

The  methods  are  based,  therefore,  upon  the  insolubility  of  some 
compound  containing  the  constituent  to  be  determined.  No  sub- 
stance is  absolutely  insoluble,  however,  and  the  amount  that  will 
dissolve  depends  upon  the  prevailing  conditions.  Consequently,  it 


2  QUANTITATIVE  ANALYSIS 

is  of  fundamental  importance  to  obtain  and  to  maintain  conditions 
of  such  a  nature  that  the  precipitate  will  always  be  under  condi- 
tions of  minimum  solubility. 

The  operations  employed  in  gravimetric  processes  include  pre- 
cipitation, filtration,  and  washing,  and  are  very  similar  to  those  used 
in  qualitative  analysis.  It  is  necessary,  however,  to  perform  them 
with  much  more  care,  neatness,  and  completeness,  for  in  the  quanti- 
tative work  the  entire  amount  of  the  constituent  must  be  precipitated, 
separated  from  the  other  substances,  and  finally  weighed.  Not 
only  are  the  operations  similar  to  those  employed  in  the  qualitative 
work,  but  the  methods  of  separation  of  the  constituents  invariably 
depend  upon  the  same  chemical  facts.  The  relations  existing 
between  these  two  branches  of  analysis  cannot  be  too  strongly  em- 
phasized. In  order  to  become  familiar  with  the  fundamental  clas- 
sifications, reactions,  separations,  and  specific  tests  for  the  identifi- 
cation of  the  elements  a  careful  and  systematic  review  of  qualitative 
analysis  should  be  made. 

To  successfully  perform  quantitative  chemical  analyses,  one  must 
learn  to  work  carefully  and  intelligently  and  also  to  do  more  than 
one  thing  at  a  time.  The  student  can  work  intelligently  only  when 
he  has  a  clear  idea  of  what  is  to  be  done  and  understands  thor- 
oughly the  chemistry  of  the  process  which  he  is  carrying  out.  Fol- 
lowing the  directions  blindly  always  brings  trouble.  Plan  the  work 
so  that  several  operations  are  going  on  at  the  same  time ;  for  exam- 
ple, while  the  samples  are  being  weighed,  the  crucibles  may  be 
heating  to  constant  weight ;  again,  while  a  precipitate  is  being  di- 
gested, the  samples  for  the  next  determination  may  be  weighed. 

Accuracy  cannot  be  attained  without  neatness.  Hence  it  is 
necessary  to  have  the  desk  and  apparatus  neat  and  clean  at  all 
times  and  to  exercise  the  greatest  care  to  keep  them  in  this  condi- 
tion. Nothing  makes  a  more  unfavorable  impression  than  dirty 
apparatus ;  moreover,  the  effect  on  the  student  himself  is  often 
demoralizing. 

NOTEBOOKS 

Care  and  neatness  are  just  as  essential  in  recording  data  as  in 
their  collection.  Record  all  of  the  data  in  a  permanent  form  just  as 
soon  as  they  are  obtained.  Use  the  notebook  provided  for  this  pur- 
pose and  make  the  entries  in  ink.  Under  no  circumstances  should 
records  be  placed  on  scraps  of  paper.  If  at  any  time  the  data 


INTR  OD  UCTION 


become  valueless  through  accident,  do  not  tear  the  leaves  out  of 
the  notebook,  but  mark  "discarded"  and  make  new  entries  on 
another  page. 

The  student  should  learn  to  record  his  results  in  a  systematic 
and  orderly  manner.  The  method  of  recording  the  data  success- 
fully used  in  the  authors'  laboratories  is  illustrated  in  Fig.  I,  which 
represents  two  pages  of  the  notebook  employed.  They  are  $"  x 
7f "  and  ruled  in  cross  section  by  lines  -J-  of  an  inch  apart. 


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FIG.  i 

The  right-hand  page  is  for  the  record  of  the  experimental  data 
and  the  report  of  the  percentage  of  the  constituent  sought.  On 
the  left-hand  page  should  be  recorded  : 

1.  The  equations  representing  all  of  the  chemical  changes  taking 
place  in  the  process. 

2.  The  calculation  of  the  results  from  the  data  collected. 

3.  A  record  of  any  special  difficulties  encountered  and  the  reme- 
dies employed. 

The  use  of  logarithm  tables  will  greatly  facilitate  the  calculations. 
Too  much  importance  should  not  be  placed  on  the  fact  that  du- 
plicates "  check,"  because  it  sometimes  happens  that  the  same  error 


4  QUANTITATIVE  ANALYSIS 

will  be  made  in  each  determination,  giving  results  which  agree,  but 
which  may  be  several  per  cent  from  the  true  value.  There  is  often 
a  tendency  for  the  student  to  "  begin  over  "  when  some  little  irreg- 
ularity has  been  introduced  into  the  procedure.  This  tendency  is 
the  cause  of  the  loss  of  much  time  and  also  results  in  the  student 
losing  confidence  in  his  work.  By  consulting  the  instructor  and 
making  a  thorough  study  of  the  conditions,  the  difficulties  may  be 
overcome,  the  exercise  carried  out  without  loss  of  time  and  a  certain 
amount  of  valuable  experience  gained.  Each  exercise  should  bring 
forth  the  best  efforts  of  the  student.  As  a  last  resort  "  begin  over." 

REAGENTS 

One  of  the  most  important  problems  with  which  the  analytical 
chemist  has  to  deal  is  the  purity  of  the  reagents.  It  is  obvious 
that  no  matter  how  good  a  manipulator  the  analyst  may  be,  if  im- 
pure reagents  are  employed,  his  results  will  be  valueless.  Young 
chemists  are  frequently  deceived  by  reagents  being  marked 
"chemically  pure,"  "for  analysis,"  etc.  For  accurate  work,  how- 
ever, such  labels  cannot  be  considered  as  a  guaranty  of  the  purity 
of  reagents.  The  analyst  can  be  sure  of  his  reagents  only  by  sub- 
jecting them  to  thorough  chemical  tests,  similar  to  those  prescribed 
by  Krauch.1 

Reagents  are  often  tested  by  making  a  "blank"  determination. 
This  consists  in  carrying  out  the  regular  determination,  omitting, 
however,  the  substances  to  be  analyzed.  The  results  of  the  blank 
are  subtracted  from  those  obtained  in  the  regular  determination. 

Attention  should  be  called  to  the  fact  that  solutions  of  ammo- 
nium hydroxide  on  standing  in  certain  reagent  bottles  attack  the 
glass,  with  the  formation  of  flaky  particles,  which  may  result  in 
spoiling  an  analysis.  Distilled  water,  moreover,  should  be  fre- 
quently tested,  as  certain  forms  of  stills  occasionally  boil  over,  with 
the  result  that  "distilled  water"  is  sometimes  more  impure  than 
the  ordinary  tap  water. 

When  removing  the  reagent  from  the  bottle,  always  pour  it  out 
and  discard  the  unused  portion.  In  order  to  insure  the  purity  of 
the  reagents  adopt  the  general  principle  of  never  introducing  a 
pipette ',  spatula,  or  other  piece  of  apparatus  into  a  reagent  bottle  and 

1  The  Testing  of  Chemical  Reagents  for  Purity^  E.  Krauch.  Translated  by  Wil- 
liamson and  Dupre. 


INTRODUCTION  5 

never  returning  the  unused  portion  of  the  reagent  to  the  bottle.  Be 
very  careful  when  handling  the  stoppers  of  the  reagent  bottles  ;  do 
not  put  them  in  such  a  position  that  the  part  which  fits  into  the 
neck  of  the  bottle  will  touch  the  desk  or  anything  else.  Cultivate 
the  habit  of  holding  the  top  of  the  stopper  between  the  fingers 
while  removing  the  reagent. 


SPECIAL  APPARATUS 


Desiccators 

For  keeping  crucibles,  samples,  etc.,  in  a  dry  atmosphere  an  ap- 
paratus known  as  a  desiccator  is  used.  For  quantitative  work  the 
form  shown  in  Fig.  2  is  very  efficient.  It  is  fitted  with  a  porce- 
lain plate  which  is  provided  with 
holes  for  four  crucibles.  Granu- 
lar calcium  chloride  which  has 
been  sifted  to  remove  the  fine  < 
particles  is  used  as  the  desiccat- 
ing agent.  When  sulphuric  acid 
is  used  for  this  purpose,  the 
bottom  of  the  desiccator  should 
be  covered  with  a  half-inch  layer 
of  asbestos  fiber,  and  this  should 
be  saturated  with  concentrated 
acid.  This  prevents  the  acid 
splashing  upon  the  crucibles, 
with  subsequent  damage  to  the 
balances.  To  render  the  desic- 
cator tight,  the  ground  part  of  the  cover  should  be  covered 
with  a  very  thin  coating  of  grease  or  vaseline. 

Trouble  is  often  caused  by  the  introduction  of  hot  crucibles  into 
the  desiccator.  This  results  in  heating  the  air,  which  expands, 
and  if  the  cover  is  then  put  into  place,  upon  cooling  a  partial 
vacuum  will  be  formed.  Upon  removing  the  cover  the  sudden 
rush  of  air  will  often  blow  the  precipitate  out  of  the  crucible.  It 
is  advisable,  therefore,  to  allow  crucibles  to  cool  for  about  a  min- 
ute before  placing  them  into  the  desiccator,  and  also  to  keep  them 
covered. 


FIG.  2 


QUANTITATIVE  ANALYSIS 


At 
to  be 
is  in 


Wash  Bottles 

least  two  wash  bottles  are  necessary  in  analytical  work,  one 
used  for  hot  and  the  other  for  cold  water.  A  form  which 
general  use  is  shown  in  Fig.  3.  A  500  or  750  c.c.  plain 
flask  makes  a  wash  bottle  of  convenient 
size.  To  facilitate  handling  the  hot  water 
bottle,  its  neck  should  be  wrapped  with  as- 
bestos  paper.  This  is  easily  done  by  thor- 
oughly  wetting  a  piece  of  asbestos  paper  and 
wrapping  it  about  the  neck  of  the  flask. 
Upon  boiling  water  in  the  flask,  the  asbes- 
tos paper  will  dry  and  adhere  tightly  to  the 
neck. 

Stirring  Rods 


FIG.  3 


For  the  removal  of  precipitates  from 
beakers  a  stirring  rod  provided  with  a 
rubber  tip  (a  " policeman")  is  used.  At 
least  four  stirring  rods  should  be  provided, 

two  13  cm.  and  two  18  cm.  in  length.     The  ends  of  these  should 

be  fused  and  rounded. 

THE  OPERATIONS   OF   QUANTITATIVE  ANALYSIS 
Sampling 

The  analyst  very  seldom  receives  substances  in  a  form  ready  for 
analysis.  It  is  more  often  the  case  that  they  come  to  him  in  the 
form  of  tubs  of  butter,  bags  of  fertilizers,  car  loads  of  ore,  etc.,  and 
he  must  obtain  a  sample  whose  value  shall  be  representative  of 
the  entire  amount.  At  first  sight  this  may  not  appear  to  present 
many  difficulties,  but  when  one  considers  the  heterogeneous  nature 
of  the  material,  it  is  evident  that  the  problem  of  obtaining  a  fair 
sample  is  one  of  the  most  difficult  with  which  the  analyst  has  to 
deal.  The  methods  of  sampling  vary  with  many  factors,  the  most 
important  of  which  are :  the  nature  and  uniformity  of  the  original 
material,  the  nature  of  the  constituent  to  be  determined,  and  the 
size  of  the  original  sample. 

Minerals  are  often  sampled  by  crushing  to  a  sufficient  fineness, 
piling  in  a  cone,  and  by  means  of  a  shovel  removing  the  diagonally 


INTRODUCTION  7 

opposite  quarters  of  the  cone.  This  removes  one  half  of  the  ma- 
terial. The  other  half  is  again  piled  into  the  form  of  a  cone  and 
the  process  repeated.  This  is  continued  until  only  a  pound  or 
two  of  the  sample  is  left,  which  is  pulverized  to  the  desired  fine- 
ness and  used  for  the  analysis.  At  any  desired  stage  the  sam- 
ple may  be  ground.  This  process  is  known  as  sampling  by 
"  quartering." 

Metals  such  as  pig  iron  are  often  nonhomogeneous,  conse- 
quently great  care  must  be  exercised  in  obtaining  samples.  This 
is  usually  done  by  taking  drillings  from  different  parts  of  the  bars 
by  means  of  a  clean  steel  drill,  mixing  these  drillings,  and  using 
them  for  the  analysis. 

Agricultural  products  are  so  diversified  that  no  general  method 
of  sampling  can  be  given.  For  certain  substances  like  butter, 
flour,  bags  of  ground  fertilizers,  etc.,  a  long  thin  tube  may  be 
used,  which  permits  the  removal  of  samples  from  the  various  parts 
of  the  barrel  or  tub.  Vegetables,  such  as  beets  and  peas,  are  usu- 
ally reduced  to  a  state  suitable  for  chemical  analysis  by  passing 
them  through  one  of  the  ordinary  kitchen  grinding  machines. 
Dry  cereals  like  corn  and  wheat  may  be  very  satisfactorily  ground 
in  an  ordinary  coffee  mill. 

Liquids  should  be  thoroughly  mixed  by  shaking  before  a  sample 
is  removed. 

REFERENCES  ON  SAMPLING 

LODGE,  R.  W.,  Notes  on  Assaying,  p.  23. 
LORD,  N.  W.,  Notes  on  Metallurgical  Analysis,  p.  9. 

WILEY,  H.  W.,  Agricultural  Analysis.     Consult  the  chapters  on  the  analysis  of 
the  different  agricultural  products. 

Weighing  Samples 

The  direct  and  the  indirect  methods  are  used  in  weighing  sam- 
ples for  analysis. 

Weighing  by  the  direct  method  consists  in  placing  the  substance 
upon  the  pan  of  the  balance,  or  upon  a  cover-glass  or  other  ves- 
sel of  known  weight,  and  adding  enough  weights  to  balance  the 
amount  of  substance  taken,  or  placing  the  weight  upon  the  pan 
and  adding  enough  substance  to  the  other  pan  to  just  balance  it. 
This  method  is  in  general  use  in  analytical  chemistry,  it  being 
particularly  adapted  to  weighing  specified  quantities  of  the  sub- 
stance. Its  application,  however,  depends  to  a  certain  extent  on 


8  QUANTITATIVE  ANALYSIS 

the  nature  of  the  substance.  Liquids  and  substances  which  absorb 
moisture  from  the  air  cannot  be  weighed  in  this  manner. 

The  indirect  method,  or  weighing  by  difference,  consists  in  plac- 
ing the  substance  into  a  stoppered  tube  or  flask,  weighing,  remov- 
ing some  of  the  substance,  and  weighing  again,  the  difference 
between  the  two  weights  being  the  weight  of  substance  taken. 
This  indirect  method  is  used  for  weighing  substances  which  readily 
take  up  or  lose  moisture,  for  liquids,  and  in  general  when  a  speci- 
fied weight  of  the  substance  is  not  necessary. 

For  weighing  substances  which  absorb  moisture  readily,  several 
devices  may  be  employed.  One  of  the  most  convenient  is  to  use 
two  cover  glasses,  the  edges  of  which  are  ground  to  fit  and  held 
tightly  together  by  a  spring  clip  as  illustrated  in  Fig.  4.  The 
weight  of  the  glasses  and  clip  being  known,  the  substance  is 
placed  upon  one  of  the  glasses,  the  other  glass  placed  over  this 
and  held  in  position  by  the  clip.  The  weight  of  the  substance 
can  then  be  obtained  without  danger  of  absorbing  moisture. 

To  determine  the  amount  of 
substances  to  be  taken  for 
analysis  requires  considerable 
experience  and  no  general  rule 
can  be  given,  as  the  quantity  to 
be  weighed  out  depends  upon 
so  many  factors.  The  amount 

of  the  constituent  to  be  deter- 

.      ,  .      , 
mined  is  of  primary  importance, 

as  in  some  cases,  where  the  percentage  is  small,  10  grams  may 
be  taken  for  the  analysis,  while  in  other  cases  0.5  gram  may 
be  sufficient.  The  nature  of  the  precipitate  is  also  an  important 
factor,  a  bulky  gelatinous  precipitate  being  hard  to  filter  and  wash. 
The  quantity  of  the  precipitate  must  not  be  too  small,  for  a  slight 
loss  due  to  manipulation  introduces  a  large  error.  Hence,  as  the 
beginner  in  quantitative  analysis  has  not  had  the  necessary  experi- 
ence which  will  guide  him  in  determining  the  amount  of  the  sub- 
stance to  be  weighed  for  analysis,  it  is  necessary  to  state  the 
quantities  to  be  used. 

Solution  and  Evaporation 

The  samples  for  analysis  are  dissolved  in  distilled  water  whenever 
possible.  If  acid  must  be  added  to  aid  in  the  solution,  a  large  excess 


INTRODUCTION  9 

over  the  amount  called  for  by  the  directions  should  be  avoided. 
An  excess  of  acid  may  dissolve  some  of  the  precipitate,  or  if  it 
must  be  neutralized  later,  it  increases  the  volume  of  the  solution 
by  using  more  ammonium  hydroxide  and  also  increases  the  amount 
of  soluble  salts  present.  In  general  the  analyst  should  try  to  find 
the  happy  medium  between  working  with  a  solution  which  is  too 
concentrated  and  one  which  is  too  dilute.  With  concentrated 
solutions  the  quantitative  separation  of  precipitates  is  frequently 
unsatisfactory,  because  of  the  occlusion  of  soluble  salts;  moreover, 
the  loss  of  a  drop  of  such  a  solution  occasions  a  serious  error.  Ex- 
tremely dilute  solutions,  on  the  other  hand,  have  the  disadvantage 
of  being  difficult  to  handle,  requiring  considerable  time  for  evapo- 
ration, and  the  large  volume  of  liquid  may  dissolve  an  appreciable 
amount  of  the  precipitate. 

Solutions  should  be  kept  covered  as  much  as  possible  to  protect 
them  from  contamination.  It  is  frequently  necessary  to  evaporate 
solutions  over  a  flame  or  on  a  water  bath,  and  here  also  the  vessel 
should  be  kept  covered. 
This  is  best  done  by 
placing  a  glass  triangle, 
shown  in  Fig.  5,  upon 
a  beaker  or  casserole, 
and  allowing  a  cover- 
glass  with  a  diameter 
a  little  larger  than  that 
of  the  vessel  to  rest  up- 
on the  triangle.  Small 
glass  hooks  which  are 
hung  over  the  side  of 
the  vessel  may  also  be 
used  to  support  the 

cover-glass.     It  should  FlG 

be  remembered  that 
alkaline  solutions  attack  glass  appreciably,  and  therefore  should 
not  be  allowed  to  stand  for  any  length  of  time  in  contact  with  glass 
vessels,  but  whenever  possible  should  first  be  made  slightly  acid. 

On  boiling  certain  solutions,  especially  those  which  contain  par- 
ticles of  suspended  matter,  much  trouble  is  often  experienced  by  a 
violent  agitation  of  the  liquid  which  is  called  "  bumping."  This  is 
caused  by  the  incomplete  diffusion  of  the  heat  applied  to  the  solu- 


10  QUANTITATIVE  ANALYSIS 

tion.  The  liquid  becomes  locally  superheated,  a  comparatively 
large  amount  of  steam  is  given  off  at  once,  and  this  is  attended  by 
an  explosion  which  may  throw  the  liquid  out  of  the  vessel.  This 
may  be  prevented  in  several  ways.  A  stream  of  gas  may  be 
passed  through  the  solution  which  keeps  the  heat  diffused,  so  that 
superheating  will  not  occur.  If  substances  with  sharp  points, 
such  as  broken  glass  or  pumice  stone,  are  placed  in  the  solution, 
the  steam  will  be  evolved  gradually  from  these  points.  For  dis- 
tilling solutions  of  this  kind  copper  flasks  are  often  used,  the 
copper  being  such  a  good  conductor  that  it  permits  the  heat  to  be 
uniformly  distributed  throughout  the  solution. 


Precipitation 

Conditions 

The  object  of  precipitation  in  quantitative  analysis  is  to  change 
the  constituent  which  is  being  determined  into  such  a  form  that  it 
can  be  easily  separated  from  the  solution  by  mechanical  means,  or 
to  remove  from  solution  a  substance  whose  presence  would  cause 
trouble  in  the  subsequent  procedure.  The  choice  of  the  form  in 
which  the  substance  is  precipitated  depends  upon  the  following 
factors : 

1.  Solubility.     The  necessity  of  the  most  complete  separation 
possible  is  obvious.     In  general,  it  is  customary  to  precipitate  a 
substance  in  its  least  soluble  form,  and  to  maintain  throughout  the 
determination  conditions  under  which  the  precipitate  will  remain 
insoluble. 

2.  Ease  of  filtration  and  washing.     The  importance  of  these 
factors  from  the  standpoint  of  economy  of  time  is  apparent. 

3.  Stability  on  drying  and  ignition  and  the  possibility  of  change 
to  a  more  stable  form  are  also  important  factors  which  must  be 
taken  into  consideration. 

In  general  the  precipitating  reagent  is  added  in  the  form  of  a 
solution.  The  method  has  several  advantages,  among  which  may 
be  mentioned  the  ease  of  control  of  the  quantity  of  the  reagent, 
and  also  the  possibility  of  detection  of  particles  of  insoluble 
foreign  matter  present  in  the  solid  reagent.  In  many  cases,  more- 
over, a  quantitative  separation  can  be  obtained  only  by  adding  the 
precipitant  in  the  form  of  a  solution.  Whenever  it  is  possible,  the 


INTR  OD  UCTION  1 1 

quantity  of  reagent  necessary  to  precipitate  the  substance  should 
be  calculated.  This  prevents  the  addition  of  an  unnecessary  ex- 
cess of  the  reagent  and  also  permits  a  correction  when  a  blank 
determination  is  made.  The  solution  must  always  be  tested  for 
complete  precipitation.  This  may  be  done  by  testing  the  super- 
natant liquid,  or  by  filtering  and  testing  a  small  portion  of  the 
filtrate. 

Many  precipitates  are  less  soluble  in  solutions  which  contain  in 
common  with  them  an  element  or  radical  (ion),  therefore  an  excess 
of  the  precipitating  reagent  is  often  added.  Thus  barium  sul- 
phate is  more  insoluble  in  barium  chloride  solution  than  in  water, 
consequently  in  the  determination  of  sulphuric  acid,  an  excess  of 
barium  chloride  is  added  to  the  solution. 

Precipitates  often  possess  the  power  of  carrying  down  or  occlud- 
ing foreign  substances.  Even  though  the  occluded  substances  are 
soluble  in  water,  it  is  often  practically  impossible  to  remove  them 
by  washing;  hence,  conditions  which  favor  occlusion  should  be 
carefully  avoided.  The  occlusion  of  the  precipitant  is  often  caused 
by  "  dumping  "  a  large  quantity  of  the  reagent  into  the  solution. 
By  stirring  the  solution  while  the  precipitant  is  being  slowly  added 
from  a  pipette  or  dropper,  this  source  of  error  may  be  avoided. 

Many  substances  when  first  precipitated  exist  in  such  a  physical 
state  that  their  separation  from  the  solution  by  means  of  a  filtering 
medium  is  almost  impossible,  owing  to  their  tendency  to  run 
through  the  filter.  Methods  have  been  devised  by  which  such 
precipitates  can  be  changed  to  forms  permitting  their  removal  by 
filtration. 

The  Enlargement  of  the  Grains  of  a  Crystalline  Precipitate 

Barium  sulphate  is  a  crystalline  precipitate  whose  grains  are  so 
small  that  they  often  run  through  the  filter.  The  grains  may  be 
enlarged  by  allowing  the  precipitate  to  stand  for  some  time  in  con- 
tact with  the  solution  at  a  temperature  close  to  the  boiling  point. 
This  may  also  be  accomplished  by  allowing  the  precipitate  to  re- 
main at  the  ordinary  temperature  in  contact  with  the  solution,  but 
the  length  of  time  must  be  greatly  extended.  This  process  is 
termed  digestion. 

Ostwald  1  gives  the  following  explanation  of  this  phenomenon : 

1  W.  Ostwald,  The  Scientific  Foundations  of  Analytical  Chemistry,  p.  22  (1900). 


12  QUANTITATIVE  ANALYSIS 

Since  every  substance  is  slightly  soluble,  a  certain  amount  of  the 
precipitate  always  remains  in  solution.  On  heating,  more  of  the 
precipitate  dissolves  and  the  smaller  particles  are  the  first  to  go 
into  solution;  the  solution  then  becomes  supersaturated  with  re- 
spect to  the  large  particles  and  a  precipitation  on  them  takes  place. 
As  the  heating  continues,  the  small  particles  are  dissolved,  and  the 
larger  particles  grow  at  their  expense.  This  process  goes  on  at  the 
ordinary  temperature,  but  much  more  slowly.  The  digestion  must 
be  carried  on  until  the  particles  are  so  large  that  they  will  not 
pass  through  the  pores  of  the  filter. 

Colloidal  Precipitates 

Many  substances,  such  as  aluminium  hydroxide  and  the  metallic 
sulphides,  form  gelatinous  or  flocculent  precipitates  and  cause 
trouble  by  running  through  the  filter.  Precipitates  of  this  kind, 
which  are  called  "colloidal,"  are  thrown  down  by  heating  the  solu- 
tion, or  by  adding  solutions  of  salts,  acids,  or  bases.  They  are 
usually  precipitated  from  hot  solutions.  The  addition  of  salts  to 
facilitate  the  precipitation  is  seldom  necessary,  as  they  are  usually 
present  in  the  solutions  in  sufficient  amount. 

Filtration 

The  process  of  filtration  has  as  its  object  the  separation  of  the 
precipitate  from  the  liquid.  For  this  purpose  a  special  grade  of 
filter  paper  is  used  which  has  been  washed  with  acids,  and  which 
on  burning  leaves  an  ash  whose  weight  may  be  neglected  in  ordi- 
nary quantitative  work.  The  size  of  the  filter  should  be  adapted  to 
the  amount  of  precipitate.  The  larger  the  filter,  the  greater  the 
quantity  of  wash  water  needed  to  remove  impurities,  consequently 
the  filter  should  be  kept  as  small  as  possible. 

The  speed  of  filtration  depends  upon 

1.  The  filtering  medium. 

2.  The  temperature  of  the  solution. 

3.  The  pressure. 

Paper  is  most  commonly  used  for  filtering,  although  in  many 
cases  asbestos  may  be  used.  Rapidity  of  filtration  depends  upon 
the  size  of  the  pores  of  the  filter. 

Since  the  internal  friction  of  water  is  less  at  high  than  at  the 


INTR  OD  UCTION  1 3 

ordinary  temperatures,  it  is  evident  that  hot  solutions  will  filter 
more  rapidly  than  those  which  are  cold. 

Filtration  is  often  accelerated  by  diminishing  the  pressure  On 
one  side  of  the  filter.  This  is  accomplished  most  frequently  by 
the  use  of  long  narrow-stemmed  funnels.  The  stem  of  the  funnel 
becomes  filled  with  a  column  of  liquid,  the  weight  of  which  draws 
the  solution  through  the  filter.  It  is  apparent  that  if  the  filter 
does  not  fit  the  funnel,  air  will  be  drawn  down  between  the  filter 
and  the  funnel  and  the  advantage  of  a  long  stem  will  be  lost.  Fil- 
tration may  also  be  hastened  by  placing  the  funnel  in  the  neck  of 
a  flask  and  diminishing  the  pressure  in  the  flask  by  means  of  a 
suction  pump.  When  this  method  is  employed,  care  must  be  taken 
that  the  filter  is  not  torn.  Its  point  must  be  supported  by  means 
of  a  well-fitting  platinum  cone,  or  by  a  cone  of  hardened  filter 
paper.  A  very  serviceable  form  of  filter  paper  used  for  this  pur- 
pose is  the  half  form  hardened  filter,  the  use  of  which  is  described 
in  Part  II,  under  the  Determination  of  Aluminium,  page  37. 

Washing 

In  order  to  obtain  a  precipitate  in  the  form  of  a  definite  chemi- 
cal compound,  the  impurities  must  be  removed.  These  impurities 
are  usually  soluble  salts  which  can  be  removed  by  washing.  It 
sometimes  happens,  however,  that  a  precipitate  contains  so  much 
impurity  that  it  must  be  dissolved  and  reprecipitated.  In  the 
second  precipitation  the  greater  part  of  the  impurity  remains  in 
solution,  while  that  remaining  with  the  precipitate  can  easily  be 
removed  by  washing.  Whenever  possible,  precipitates  should  be 
washed  several  times  by  decantation,  as  impurities  are  much  more 
rapidly  removed  in  this  way.  When  washing  the  precipitate  on 
the  filter,  the  water  should  be  allowed  to  drain  from  the  precipitate 
before  the  next  portion  of  water  is  added,  as  the  impurities  are  dis- 
solved more  rapidly  and  with  the  use  of  the  minimum  quantity  of 
wash  water.  The  fact  should  be  borne  in  mind  that  all  precipitates 
are  soluble  to  some  extent,  consequently  a  large  amount  of  wash 
water  may  dissolve  enough  of  the  substance  to  introduce  an  appre- 
ciable error.  Enough  wash  water  should  be  used  to  remove  the 
impurities,  but  no  more.  The  washings  are  usually  tested  for  some 
specific  impurity,  and  when  this  is  removed,  it  is  assumed  that  the 
other  substances  have  also  been  washed  out.  In  the  determina- 


14  QUANTITATIVE  ANALYSIS 

tion  of  chlorine,  for  example,  the  precipitate  contains  silver  nitrate 
and  sodium  nitrate  as  impurities.  It  is  washed  until  free  from  sil- 
ver nitrate  on  the  assumption  that  by  that  time  it  will  also  be  free 
from  sodium  nitrate.  The  wash  water  must  always  be  tested  to 
be  sure  that  the  impurities  are  removed  and  tinder  no  circum- 
stances may  this  be  neglected. 

Colloidal  precipitates  on  being  washed  frequently  return  to  the 
finely  divided  state,  and  run  through  the  filter.  This  may  be  pre- 
vented by  using  wash  water  which  contains  a  salt  which  will  vola- 
tilize when  the  precipitate  is  ignited.  Ammonium  nitrate  is  often 
used  for  this  purpose. 

Drying  and  Igniting  Precipitates 

For  the  removal  of  the  last  portion  of  wash  water,  the  precipi- 
tate is  usually  dried  in  an  air  bath  which  is  maintained  at  a  tem- 
perature of  110°.  To  prevent  contamination  from  dust,  the  funnel 
should  be  covered  with  a  wet  qualitative  filter  the  edges  of  which 
are  folded  down  over  the  edge  of  the  funnel.  Gooch  crucibles  may 
be  conveniently  dried  by  placing  them  into  small  covered  beakers, 
and  then  putting  them  into  a  hot  closet. 

Filters  are  ignited  by  the  following  methods  : 

1.  By  placing  them  with  the  precipitate  into  a  crucible,  allow- 
ing access  of  air,  and  heating  until  the  carbonaceous  matter  is  con- 
sumed.   This  method  is  used  when  the  burning  filter  paper  has  no 
action  on  the  precipitate. 

2.  By  removing  the  precipitate  as  completely  as  possible  from 
the  filter,  igniting  the  filter  paper  upon  a  platinum  wire,  so  that 
the  ash  will  fall  into  a  crucible,  then  adding  the  main  part  of  the 
precipitate  to  the  ash.     This  method  is  employed  when  the  pre- 
cipitates are  of  such  a  nature  that  the  burning  filter  paper  will 
change  their  chemical  composition. 

Crucibles 

For  the  ignition  of  many  precipitates  porcelain  crucibles  may  be 
used.  They  have  the  disadvantage  of  being  easily  broken ;  more- 
over, the  thickness  of  the  porcelain  makes  it  impossible  to  heat 
the  precipitate  to  a  high  temperature.  On  the  other  hand,  they 
are  cheap  and  are  impervious  to  the  reducing  gases  of  the  burner. 

For  many  purposes  platinum  crucibles  are  indispensable.     Their 


INTR  OD  UCTION  1 5 

advantages  lie  in  their  resistance  to  the  ordinary  reagents,  also  in 
the  fact  that  they  permit  the  precipitate  to  be  heated  to  an  ex- 
tremely high  temperature.  Their  use  is  restricted  by  conditions 
described  under  the  following  paragraph. 

The  Use  and  Care  of  Platinum  1 

It  is  important  to  remember  that,  although  platinum  is  not  oxidized  in  the  air 
at  any  temperature,  nor  attacked  by  any  single  acid,  yet  there  are  many  substances 
that  attack  and  combine  with  it  at  comparatively  low  temperatures. 

Platinum  should  never  be  used  in  solutions  containing  free  chlorine,  bromine, 
iodine,  or  ferric  chloride,  as  it  is  attacked  under  these  conditions.  The  caustic 
alkalies,  the  alkaline  earths,  nitrates  and  cyanides,  and  especially  the  hydrates  of 
barium  and  lithium,  attack  platinum  at  a  red  heat,  although  the  alkaline  car- 
bonates have  no  effect  at  the  highest  temperatures.  Sulphur,  in  the  presence  of 
alkalies,  has  no  action,  but  phosphorus  and  arsenic  attack  platinum  when  heated 
with  it. 

Organic  matter  containing  phosphorus  should  not  be  ignited  in  platinum  dishes, 
as  it  affects  the  platinum  seriously.  Direct  contact  of  platinum  with  burning 
charcoal  should  be  avoided,  since  the  silicon  reduced  from  the  charcoal  ashes 
unites  with  platinum,  making  it  brittle  and  liable  to  fracture.  Also  contact  with 
compounds  of  the  easily  reducible  metals  is  especially  dangerous  at  high  tem- 
peratures, as  alloys  having  a  low  fusing  point  are  readily  formed  with  platinum. 
This  is  especially  true  of  lead.  Moreover,  the  red-hot  crucible  should  never  be 
seized  with  brass  crucible  tongs,  as  hot  platinum  dissolves  copper,  and  the  cru- 
cible is  often  stained  in  this  way. 

When  gas  is  used,  care  should  be  taken  to  have  the  supply  of  air  sufficient  to 
insure  complete  combustion,  since,  with  a  flame  containing  free  carbon,  the  plati- 
num suffers  deterioration  by  the  formation  of  a  carbide  of  platinum,  which,  oxi- 
dizing later,  blisters  the  metal.  For  this  reason,  also,  the  inner  cone  or  reducing 
flame  should  not  be  in  contact  with  the  metal.  The  loosening  effect  of  the  Bun- 
sen  flame  upon  the  surface  of  platinum  exposed  to  its  action  produces  the  familiar 
gray  appearance  which  cannot  be  removed  except  by  burnishing.  Platinum  tri- 
angles often  become  gray  and  very  brittle  from  the  same  cause.  Systematic 
application  of  moist  sea  sand  to  all  articles  affected  in  this  way,  after  use,  will 
keep  them  in  prime  condition  and  materially  prolong  their  life,  with  but  a  trifling 
loss  in  weight. 

Hot  crucibles  should  not  be  plunged  into  cold  water  to  loosen  fusions  which 
they  contain,  nor  should  the  platinum  be  worked  between  the  fingers  for  the  same 
purpose.  If  possible,  each  crucible  should  be  provided  with  a  wooden  form  which 
will  aid  materially  in  keeping  it  in  the  proper  shape. 

Every  careful  analyst  of  necessity  uses  clean  utensils.  The  habit  of  cleaning 
and  polishing  platinum  dishes  immediately  after  using  them  is  easily  formed,  and 
repays  the  user  with  increased  confidence  in  his  work  as  well  as  in  the  prolonged 
life  of  the  article.  Rubbing  the  surface  of  platinum  with  moist  sea  sand  (round 

1  From  directions  furnished  by  Baker  &  Co. 


1 6  QUANTITATIVE  ANALYSIS 

grains  only)  applied  with  the  finger,  serves  to  remove  most  impurities  and  to  pol- 
ish the  metal  without  material  loss. 

Fusing  potassium  bisulphate  or  borax  in  the  platinum  vessel  and  then  boiling 
it  in  water  and  polishing  it  with  sand,  as  above,  is  recommended  by  Gmelin. 
When  it  is  desired  to  clean  the  outer  surface  of  dishes  in  this  manner,  they 
must  be  placed  in  dishes  of  sufficient  size  to  allow  the  fused  flux  to  envelop 
completely  the  article  to  be  cleaned.  Sodium  amalgam  possesses  the  property 
of  wetting  platinum  without  amalgamating  with  it,  even  when  other  metals 
are  purposely  added  to  the  amalgam.  This  substance,  therefore,  is  useful  for 
effecting  a  quick  and  thorough  cleansing  of  platinum.  The  amalgam  is  gently 
rubbed  upon  the  metal  with  a  cloth  and  then  moistened  with  water,  which  oxi- 
dizes the  sodium  and  leaves  the  mercury  free  to  alloy  with  foreign  metals.  The 
mercury  is  then  wiped  off,  and  the  dish  is  cleaned  and  polished  with  sand.  If 
the  existence  of  a  base  metal  alloyed  with  the  platinum  is  suspected,  immerse  the 
article  in  question  first  in  boiling  hydrochloric  acid  for  a  few  minutes,  then,  after 
a  thorough  rinsing  with  clean  water,  immerse  it  in  boiling  nitric  acid  free  from 
chlorine.  If  the  dish  is  unaffected  in  weight  or  appearance,  and  the  acid  baths 
fail  to  give  reactions  for  the  base  metals,  their  absence  in  appreciable  quantities 
is  assured. 

The  Balance 

Quantitative  analysis  may  be  said  to  have  had  its  birth  with  the 
introduction  of  the  balance  into  the  chemical  laboratory.  The  bal- 
ance is,  therefore,  one  of  the  most  important  pieces  of  apparatus 
which  'the  chemist  uses,  and  in  order  to  do  intelligent  work  a 
thorough  knowledge  of  the  principles  of  construction  and  of  its 
essential  parts  is  necessary. 

The  balance  is  used  to  determine  the  weight  of  substances,  and 
this  is  accomplished  by  utilizing  the  force  of  gravity,  which  acts  as 
parallel  forces  on  the  bodies  to  be  weighed.  When  these  forces 
are  equal,  the  bodies  are  said  to  have  equal  weights.  The  weight 
of  a  body,  i.e.,  the  measure  of  the  earth's  attraction  for  it,  bears  a 
definite  relation  to  the  quantity  of  matter  it  contains,  that  is,  to  its 
mass.  The  process  of  weighing  is,  therefore,  a  determination  of 
the  relation  between  masses.  The  weights  employed  are  standard 
masses,  and  the  process  of  weighing  consists  in  comparing  the  at- 
traction of  the  earth  for  the  standard  mass  with  its  attraction  for 
the  mass  of  the  substance  whose  weight  is  to  be  determined.  The 
force  of  gravity  is  not  the  same  at  all  places  on  the  surface  of  the 
earth,  but  varies  with  the  latitude  and  with  the  elevation  above  sea 
level.  The  mass  of  a  body  does  not  vary  whatever  its  location  on 
the  surface  of  the  earth,  hence,  the  standard  mass  (weight)  and 


INTRODUCTION  17 

the  body  to  be  weighed  will   be  affected  alike  by  a  change  in 
location. 

The  Construction  of  the  Balance 

The  usual  analytical  balance  is  essentially  a  lever  supported  at 
its  middle  point  on  a  frictionless  fulcrum  and  resting  in  a  state  of 
stable  equilibrium.  The  lever,  which  is  known  as  the  beam  of 
the  balance,  is,  therefore,  divided  into  two  arms  which  have  as 
nearly  as  possible  the  same  length  and  weight.  At  the  ends  of  the 
beam  are  suspended  two  pans  by  means  of  hooks  or  stirrups  which 
rest  on  bearings  similar  to  that  on  which  the  beam  rests.  The 
essential  parts  of  the  balance  are : 

1.  The  beam.     This  should  be  in  a  state  of  stable  equilibrium 
and  respond  readily  to  small  differences  in  load. 

2.  The  bearings.    Both  the  central  and  terminal  bearings  consist 
of  a  knife-edge  and  a  plane  or  concave  surface.     They  should  be 
made  of  agate. 

3.  The  pans  and  their  supporting    devices.     They   should   be 
made  of  non-corroding  metal  and  constructed  as  light  as  possible. 

To  fulfill  the  requirements  of  the  chemist,  the  balance  should  be 
accurate  and  sensitive.  The  construction  of  the  essential  parts  of 
the  balance  determines  its  character. 

Position  of  the  Center  of  Gravity 

The  condition  that  the  beam  be  in  a  position  of  stable  equilib- 
rium is  fulfilled  when  the  center  of  gravity  is  below  the  axis,  that  is, 
below  the  line  of  contact  between  the  central  knife-edge  and  the 
plane  on  which  it  rests.  For,  if  the  center  of  gravity  were  in  this 
axis,  the  condition  of  equilibrium  would  be  indifferent,  and  the 
beam  would  not  oscillate,  but  would  remain  in  any  position  in 
which  it  was  placed.  If,  on  the  other  hand,  the  center  of  gravity 
were  above  the  axis,  the  equilibrium  would  be  unstable,  and  if  the 
beam  were  once  removed,  it  would  not  return  to  its  original  posi- 
tion. 

By  sensitiveness  is  understood  the  ease  with  which  the  beam 
moves.  The  sensitiveness  of  a  balance  is  usually  defined  as  the 
angle  through  which  the  beam  will  turn  for  a  given  difference  of 
load  upon  the  two  pans.  It  depends  mainly  upon  the  nearness  of 
the  center  of  gravity  to  the  axis.  Every  balance  is  so  constructed 
c 


i8  QUANTITATIVE  ANALYSIS 

that  the  degree  of  sensitiveness  can  be  regulated  within  certain 
limits  by  adjusting  the  distance  between  the  two.  This  is  accom- 
plished by  raising  or  lowering  a  movable  bob  upon  the  pointer,  or 
a  nut  upon  the  post  above.  The  time  of  oscillation  increases  with 
the  sensitiveness.  It  is  possible  for  the  oscillations  to  be  so  slow 
that  a  considerable  amount  of  time  will  be  lost  in  weighing.  The 
time  of  an  oscillation  should  be  from  ten  to  fifteen  seconds. 

The  Knife-edges 

The  terminal  knife-edges  of  a  good  balance  should  be  parallel 
to  each  other  and  to  the  central  knife-edge.  They  should  lie  in 
the  same  plane  with  the  central  knife-edge,  or  very  slightly  above 
it.  By  loading  the  pans  of  a  balance  there  is  a  change  in  the  po- 
sition of  the  center  of  gravity  with  respect  to  the  axis,  and  it  has 
been  shown  that  a  change  in  the  relative  position  of  the  axis  and 
the  center  of  gravity  affects  the  sensitiveness.  If  the  terminal 
knife-edges  are  below  the  central  one,  loading  the  pans  lowers  the 
center  of  gravity  still  further  and  thereby  decreases  the  sensitive- 
ness. 

The  Beam 

The  beam  is  one  of  the  main  factors  in  establishing  the  sensi- 
tiveness of  a  balance.  The  beam  must  be  as  rigid  as  possible,  for 
by  loading  the  balance  the  terminal  knife-edges  would  be  lowered 
if  the  beam  should  bend,  and  consequently  the  sensitiveness  of  the 
balance  would  be  decreased.  As  no  beam  is  absolutely  rigid,  it 
is  practicable  to  place  the  terminal  knife-edges  slightly  above  the 
central  one  and  so  regulate  their  distance  from  the  axis  that  the 
maximum  load  of  the  balance  cannot  produce  indifferent  or  un- 
stable equilibrium.  If  the  arms  of  the  beam  are  heavy,  it  will  re- 
quire a  larger  weight  at  one  end  (in  one  pan)  to  produce  a  given 
deflection  than  if  the  beam  were  lighter.  Hence,  it  is  apparent 
that  the  sensitiveness,  which  is  the  angle  of  deflection,  depends 
upon  the  weight  of  the  beam — the  lighter  the  beam,  the  greater 
the  sensitiveness ;  therefore,  the  beam  should  be  constructed  as 
light  as  possible.  It  is  very  evident,  from  the  principles  of  the 
lever,  that  in  the  case  of  two  levers  (other  things  being  equal),  the 
one  with  the  longer  arms  will  be  moved  by  a  smaller  weight  than 
the  one  with  short  arms.  The  balance  with  the  longer  beam  will 


INTRODUCTION  19 

have  a  greater  angle  of  deflection  than  the  short-armed  beam ; 
therefore,  the  longer  the  beam,  the  greater  the  sensitiveness.  But 
here,  too,  there  is  a  limit,  for  it  is  difficult  to  get  a  long  beam  that 
is  sufficiently  rigid  without  giving  too  much  weight ;  further,  if  it  is 
too  sensitive,  there  may  be  too  much  time  lost  in  weighing.  From 
these  facts,  there  has  grown  up  the  rivalry  between  the  long  and 
short-armed  balances.  By  the  introduction  of  aluminium  in  the 
manufacture  of  balance  beams  and  pans,  we  are  enabled  to  get  a 
medium  length  rigid  beam  that  is  very  light,  thus  combining  the 
strong  points  of  the  other  two  styles  of  balances. 

The  pans  are  suspended  from  the  ends  of  the  beam  upon  the 
terminal  knife-edges  by  means  of  hooks  or  stirrups,  which  permit 
them  to  hang  perpendicularly  and  thus  not  increase  the  length  of 
the  beam.  Friction  at  the  terminal  knife-edges  affects  very  seri- 
ously the  sensitiveness  of  the  balance. 

The   Weights 

The  capacity  of  the  analytical  balances  is  usually  200  grams; 
i.e.,  the  maximum  weight  which  may  be  placed  on  each  pan.  It  is 
very  rarely,  however,  that  the  analyst  weighs  objects  having  a 
greater  weight  than  100  grams.  Hence,  sets  of  weights  from  50 
grams  to  5  milligrams,  having  a  total  weight  of  about  100  grams, 
are  usually  provided  with  each  balance.  The  weights  from  one 
gram  up  are  made  of  brass  and  are  often  gold  plated,  while  the 
fractional  weights  are  of  platinum  made  in  the  form  of  a  square 
with  one  edge  turned  up  to  facilitate  handling.  Milligrams  and 
fractions  thereof  are  measured  by  a  small  weight  called  a  rider. 
This  is  placed  upon  the  beam,  which  is  graduated  from  the 
point  directly  above  the  central  knife-edge  out  to  the  point  directly 
above  the  terminal  knife-edge.  The  number  of  divisions  depends 
upon  the  make  of  the  balance,  there  usually  being  50,  60,  or  100. 
When  5,  6,  and  10  milligram  riders  are  used  respectively,  each  di- 
vision will  represent  -fa  of  a  milligram.  By  means  of  a  rod  carry- 
ing a  finger  the  rider  can  be  conveniently  placed  at  will  on  any 
division  on  the  beam.  Owing  to  the  different  graduations  on  the 
beams  of  balances  of  different  makes,  much  confusion  may  arise 
from  use  of  riders  obtained  from  the  various  manufacturers.  Al- 
ways be  sure  that  the  rider  employed  when  placed  on  the  proper 
division  will  balance  the  5 -milligram  weight. 


20  QUANTITATIVE  ANALYSIS 

Summary  of  Precautions  to  be  Observed  in    Weighing 

1.  Sit  directly  in  front  of  the  center  of  the  balance  so  as  to 
avoid  parallax  while  observing  the  movements  of  the  pointer. 

2.  See  that  the  balance  is  level. 

3.  See  that  the  rider  will  be  free  from  the  beam  when  it  is 
swinging. 

4.  Release  and  arrest  of  the  beam  and  pans. 

a.  Release  the  beam  before  releasing  the  pans. 

b.  Release  and  arrest  the  beam  with  a  slow,  steady  move- 

ment, avoiding  jerky  movements  which  are  sure  to  in- 
jure the  knife-edges. 

c.  The  beam  should  be  arrested  only  when  it  is  in  a  hori- 

zontal position. 

d.  Avoid  giving  the  pans  a  rotatory  motion  in  the  horizon- 

tal direction,  and  all  other  motions  which  would  cause 
the  knife-edges  to  scrape  on  their  bearings. 

e.  If  the  beam  does  not  begin  swinging  as  soon  as  it  is 

released,  set  it  in  motion  by  placing  the  rider  on  the 
four  or  five  milligram  division  and  raising  it  again. 

5.  Never  place  an  object,  not  even  the  smallest  weight,  upon  the 
pan,  or  remove  one  from  it,  unless  the  beam  and  pans  are  supported, 
i.e.,  arrested. 

6.  Always  place  the  weights  and  objects  to  be  weighed  in  the 
middle  of  the  pans.     Long  tubes  and  other  objects  which  cannot 
be  easily  centered  on  the  pan,  may  be  suspended  from  the  hooks 
above  the  pans. 

7.  Handle  all  the  weights  with  the  tweezers  provided  for  this 
purpose,  and  never  use  these  tweezers  for  any  other  purpose. 

8.  Objects  to  be  weighed  must  never  be  placed  in  direct  con- 
tact with  the  pans  unless  they  are   metallic,  glass,  or  porcelain. 
Hot  objects  cannot  be  accurately  weighed,  owing  to  the  upward 
draughts  they  create  about  the  pan  on  which    they  rest.     They 
may  also  heat  the  beam  and  thus  produce  a  change  in  the  relative 
length  of   the  arms.     Hygroscopic   and  volatile  substances,  and 
those  that  absorb  carbon  dioxide  from  the  air,  should  be  weighed 
in  closed  vessels  which  must  be  opened  a  moment  before  weighing. 

9.  Weighing  is  an  accurate  operation :  never  do  it  when  in  a 
hurry. 


INTRODUCTION  21 

10.  Be  sure  that  the  reading  of  the  weights  is  taken  correctly. 
Check  by  two  readings ;  first,  read  the  weights  from  the  vacant 
spaces  where  they  are  kept,  and,  second,  read  again  as  the  weights 
are  returned  to  their  places. 

11.  Never  leave  the  beam  resting  on  the  knife-edge  when  not 
in  use,  and  never  leave  the  weights  on  the  pan,  but  always  return 
them  to  their  places. 


PART    II 

GRAVIMETRIC   ANALYSIS 

EXERCISES  WITH   THE   BALANCE 

EXERCISE  I 
Determination  of  the  Time  of  Vibration 

Procedure.  —  Dust  the  beam  and  pans  very  carefully  with  a 
camel's-hair  brush.  Cautiously  release  the  beam  and  then  the 
pans.  After  the  beam  has  oscillated  long  enough  to  recover  from 
the  effects  of  any  jar  it  may  have  received  when  released,  deter- 
mine the  time  required  for  the  pointer  to  make  ten  excursions  past 
the  central  or  zero  part  of  the  ivory  scale.  One  tenth  of  this  is 
the  Time  of  Vibration.  Determine  the  time  of  vibration  when  the 
pointer  makes  long,  short,  and  medium  excursions. 

Note. — Time  of  vibration  varies  with  the  load.  It  also  varies  with 
the  length  of  the  beam,  —  the  shorter  the  beam,  other  things  being 
equal,  the  shorter  the  time.  The  time  of  vibration  for  a  balance 
with  a  given  load  is  a  measure  of  the  sensitiveness.  Much  can 
be  learned  concerning  the  quality  and  condition  of  a  balance  by 
simply  determining  the  time  of  vibration  under  different  loads. 

EXERCISE  II 
Determination  of  the  Zero  Point 

Procedure.  —  Release  the  beam  and  then  the  pans,  and  after  a 
few  excursions  of  the  pointer,  begin  to  note  and  record  the  num- 
ber of  scale  divisions  the  pointer  passes  over,  estimating  to  tenths 
of  a  division.  Place  the  readings  to  the  right  in  a  column  headed 
R,  and  those  to  the  left  in  one  headed  L.  Take  a  number  of 
observations,  three  or  four  on  one  side  and  a  greater  number  by 
one  on  the  other  side.  Add  the  two  columns  and  divide  each 
sum  by  the  number  of  observations  taken  on  that  side.  The  re- 
sults represent  the  average  excursion  of  the  pointer.  Now  add 
these  two  and  divide  by  two  and  subtract  the  quotient  from  the 

22 


GRA  VIMETR1C  ANAL YSIS  23 

greater  of  the  average  excursions.  The  result  gives  the  distance 
from  the  center  of  the  scale,  on  the  side  of  the  longer  swing  at 
which  the  pointer  would  stop  if  the  beam  were  to  come  to  rest,  i.e., 
the  Zero  Point.  If  the  zero  point  is  found  to  be  more  than  half 
a  division  from  the  middle  line  of  the  scale,  it  should  be  brought 
nearer  by  adjusting  the  nut  on  the  screw  projecting  from  the  end 
of  the  beam.  Exact  adjustment  is  not  essential,  as  the  relative 
length  of  the  arms  is  constantly  changing.  Do  not  adjust  the  bal- 
ance, but  ask  the  instructor  to  do  so. 

Note.  —  Lack  of  constancy  of  the  zero  point  may  be  due  to 
changes  of  temperature,  defective  condition  of  the  knife-edges,  or 
to  jarring. 

EXERCISE  III 

Determination  of  the  Sensitiveness 

Procedure.  —  Determine  the  zero  point  without  a  load.  Now 
place  the  rider  on  the  one  milligram  division  (the  first  numbered 
division)  of  the  arm  and  again  determine  the  zero  point.  The  dis- 
tance between  these  two  zero  points  is  usually  designated  the  Sen- 
sitiveness of  the  balance. 

Note.  —  A  balance  is  sufficiently  sensitive  for  ordinary  quantita- 
tive work  when  a  weight  of  one  milligram  changes  the  zero  point 
three  divisions. 

EXERCISE  IV 

Weighing  by  the  Usual  Method 

Procedure.  —  Obtain  the  object  to  be  weighed  and  remove  any 
moisture  by  means  of  a  clean  linen  handkerchief.  Determine  the 
zero  of  the  balance.  Place  the  object  in  the  center  of  the  left 
pan  and  in  the  center  of  the  right-hand  pan  a  weight  which  is 
estimated  to  be  approximately  the  weight  of  the  object.  Release 
the  beam  until  it  is  evident  which  way  it  swings,  then  slowly  sup- 
port it  again.  In  case  the  weight  added  is  nearly  equal  to  the 
weight  of  the  object,  it  may  be  necessary  to  release  the  pans  in 
order  to  see  which  way  the  beam  swings  and  which  is  the  heavier, 
the  weight  or  the  object.  If  the  weight  is  too  heavy,  remove  it 
and  add  the  next  lighter  weight,  following  the  order  in  which  the 
weights  are  placed  in  the  box.  When  the  beam  shows  that  the 


24  QUANTITATIVE  ANALYSIS 

weight  added  is  just  too  light,  add  to  it  the  next  smaller  weight. 
If  this  is  too  heavy,  remove  it  and  make  trials  until  one  is  found 
which  again  gives  a  total  weight  which  is  just  too  light.  Continue 
this  series  of  trials  until  all  of  the  necessary  weights  from  the  box 
have  been  added,  then  place  the  rider  at  different  points  on  the 
arm  until  one  is  reached  at  which  the  zero  point  is  found  to  coin- 
cide with  that  previously  found  for  the  unloaded  balance.  Begin- 
ning with  the  largest  weight,  read  them  from  the  vacant  spaces  in 
the  weight  box  and  record  the  values,  expressing  them  in  grams 
and  decimals  thereof.  Do  not  neglect  to  notice  the  position  of 
the  rider  on  the  beam  and  include  this  value.  Then  check  this 
by  reading  the  values  of  the  weights  as  they  are  removed  from 
the  balance  pan. 

GRAVIMETRIC   DETERMINATIONS 

EXERCISE  V 
The  Determination  of  Chlorine 

Procedure.  —  Clean  a  weighing  tube  thoroughly,  be  sure  that 
it  is  dry,  and  provide  it  with  a  well-fitting  cork.  Take  the  tube  to 
the  instructor's  office  and  obtain  the  substance  to  be  analyzed. 
With  a  clean  linen  handkerchief  remove  any  particles  of  substance 
which  adhere  to  the  cork  and  the  inside  of  the  tube  as  far  as  the 
cork  extends.  Clean  two  No.  3  beakers,  mark  them  I  and  2 
respectively,  and  take  them  and  the  weighing  tube  into  the  balance 
room.  Be  sure  that  the  outside  of  the  tube  is  clean,  then  weigh  it 
on  the  balance  which  has  been  assigned,  and  record  this  weight 
in  the  notebook  in  the  manner  indicated  on  page  3.  Hold  the 
weighing  tube  over  beaker  No.  I,  carefully  remove  the  cork  by  a 
rotary  motion,  and  by  rotating  the  tube  introduce  0.2  to  0.4  gram 
of  the  substance  into  the  beaker.  Tap  the  tube  gently  to  remove 
any  loose  particles,  replace  the  cork,  and  weigh  the  tube  and  its 
contents.  If  much  more  than  0.4  gram  has  been  taken,  it  will  be 
necessary  to  weigh  out  another  portion  into  a  clean  beaker. 
Weigh  another  portion  of  the  substance  into  beaker  No.  2.  Be 
sure  that  the  numbers  on  the  beakers  correspond  with  the  proper 
weights  of  substances  recorded  in  the  notebook. 

Add  to  each  portion  of  the  substance  about  100  c.c.  of  cold 
distilled  water  and  a  slight  excess  of  dilute  nitric  acid.  .  This 


GRA  VIMETRIC  ANAL  YSIS  2  5 

should  be  done  by  making  the  solution  just  acid  with  dilute  nitric 
acid.  Use  litmus  paper  to  test  the  acidity  of  the  solution  and  be 
sure  to  wash  the  liquid  adhering  to  the  paper  back  into  the  beaker 
by  means  of  water  from  the  wash  bottle.  Add  to  the  beaker  an 
excess  of  two  or  three  cubic  centimeters  of  dilute  nitric  acid. 
Now  add  a  clear  solution  of  silver  nitrate,  drop  by  drop,  allowing 
it  to  run  down  the  side  of  the  beaker  and  stirring  continuously 
with  a  glass  rod.  Continue  this  until  no  more  precipitate  is  seen 
to  form.  Stir  the  solution  vigorously  until  the  particles  of  the 
precipitate  collect  in  a  curdy  mass,  then  test  for  complete  precipi- 
tation by  adding  a  few  drops  of  the  silver  nitrate  to  the  solution. 
Heat  the  contents  of  the  beaker  until  the  temperature  is  near  the 
boiling  point,  and  continue  the  stirring  until  the  liquid  is  practi- 
cally clear. 

Place  a  9  cm.  ashless  filter  paper  into  a  funnel,  folding  it  so 
that  it  will  fit  exactly.  If  the  angle  of  the  funnel  is  exactly  60°, 
the  filter  will  fit  if  it  is  carefully  folded  in  the  usual  manner.  If 
it  does  not  fit,  it  will  be  necessary  to  adjust  it  to  the  funnel  by 
allowing  one  edge  to  lap  over  the  other.  By  holding  the  filter  in 
place  with  the  finger  and  wetting  it,  it  will  adhere  to  the  side  of 
the  funnel.  Be  sure  that  the  top  edge  fits  snugly  to  the  funnel. 

Now  filter  by  pouring  the  liquid  down  a  glass  stirring  rod, 
held  tightly  against  the  lip  of  the  beaker  and  reaching  nearly  to 
the  bottom  of  the  filter.  Wash  the  precipitate  by  decantation, 
using  portions  of  about  20  c.c.  distilled  water  acidified  with  nitric 
acid.  This  should  be  done  by  stirring  the  precipitate  in  order  to 
disintegrate  it,  allowing  it  to  settle  and  pouring  off  the  super- 
natant liquid  as  described  above.  Repeat  this  process  three  or 
four  times.  Replace  the  beaker  containing  the  filtrate  with  a 
clean  beaker,  and  transfer  the  precipitate  to  the  filter  by  aid  of 
a  stream  from  the  wash  bottle  which  should  contain  water  acidi- 
fied with  nitric  acid.  This  may  be  accomplished  by  holding  the 
beaker  in  an  inclined  position  with  the  lip  down,  with  stirring  rod 
pressed  firmly  against  the  lip.  By  means  of  a  jet  of  water  from 
the  wash  bottle  the  precipitate  may  be  washed  down  the  rod  and 
into  the  filter.  If  it  cannot  be  entirely  removed  in  this  manner, 
then  by  means  of  a  stirring  rod  provided  with  a  policeman  the 
precipitate  can  be  loosened  from  the  beaker  and  then  removed. 
Be, sure  that  all  of  the  precipitate  is  completely  removed.  This 
may  be  ascertained  by  cleaning  the  outside  of  the  beaker  and  then 


26  QUANTITATIVE  ANALYSIS 

observing  it  when  held  toward  the  light.  When  the  precipitate 
has  been  completely  removed  from  the  beaker,  continue  the 
washing  by  directing  a  stream  of  the  cold  acidified  water  from  the 
wash  bottle  against  the  top  of  the  filter.  Conduct  the  stream 
around  the  edge  of  the  filter  until  the  water  has  filled  it  to  within 
one  quarter  of  an  inch  from  the  top.  Add  no  more  wash  water 
until  that  in  the  filter  has  run  through.  Continue  washing  in  this 
way  until  the  impurities  are  all  removed.  This  can  best  be  ascer- 
tained by  collecting  about  3  c.c.  of  the  wash  water  in  a  test  tube, 
acidifying  with  nitric  acid,  and  adding  a  drop  of  dilute  hydro- 
chloric acid.  If  no  turbidity  results,  the  washing  is  complete. 
Allow  the  funnel  to  drain  for  a  few  minutes,  cover  the  top  with 
a  piece  of  wet  qualitative  filter  paper,  label  properly,  and  place 
it  into  a  drying  closet  which  is  heated  to  1 10°. 

While  carrying  out  the  foregoing  steps  of  precipitation  and 
filtration,  the  student  will  find  time  to  prepare  in  the  following 
manner  two  porcelain  crucibles  in  which  to  weigh  the  precipitates. 
Clean  two  porcelain  crucibles  and  covers  and  mark  them  I  and  2 
respectively  by  means  of  a  blue  pencil.  Place  the  crucibles  on 
clean  clay  triangles  which  are  resting  on  tripods,  and  heat  them 
for  fifteen  minutes  to  the  full  heat  of  the  adjustable  burner. 
Remove  the  burners,  allow  the  crucibles  to  cool  for  about  a 
minute,  place  them  into  a  desiccator,  and  weigh  them  after  they 
have  cooled  to  room  temperature,  which  usually  takes  about 
fifteen  minutes.  Heat  again  and  reweigh.  Continue  this  until 
two  consecutive  weighings  are  not  more  than  0.2  milligram  apart. 
The  crucible  has  now  a  constant  weight. 

When  the  contents  of  the  funnels  are  dry,  remove  from  the  hot 
closet.  Place  side  by  side  on  the  desk  two  pieces  of  glazed  paper 
about  six  inches  square,  the  edges  of  which  should  be  smooth. 
Remove  the  filter  from  the  funnel  by  inserting  the  small  blade  of 
a  penknife  between  the  paper  and  the  funnel.  Carefully  invert 
the  filter  over  one  of  the  pieces  of  glazed  paper.  Loosen  the 
precipitate  by  gently  squeezing  and  rubbing  between  the  fingers. 
When  most  of  the  precipitate  is  separated,  reverse  the  filter,  and 
loosen  any  portions  of  the  silver  chloride  still  remaining  by  carefully 
rubbing  the  sides  of  the  filter  together.  Allow  the  portion  that  is 
thus  detached  to  fall  upon  the  glazed  paper  and  cover  with  a 
cover-glass.  Fold  the  filter  so  that  it  will  form  a  half  circle,  place 
it  upon  the  other  sheet  of  glazed  paper,  and  fold  it  into  a  narrow 


GRAVIMETRIC  ANALYSIS 


27 


flattened  roll,  beginning  with  the  straight  edge.  Now  bring  the 
two  ends  together  and  wrap  a  platinum  wire  securely  around 
them.  In  this  way  the  central  parts  of  the  filter,  to  which  small 
particles  of  the  precipitate  still  adhere,  are  thoroughly  enveloped 
by  the  exterior  parts  so  that  in  the  subsequent  burning  nothing 
can  be  easily  lost.  By  means  of  the  wire  hold  the  filter  paper  over 
the  proper  weighed  crucible  which  has  been  placed  upon  the 
glazed  paper,  and  ignite  by  means  of  a  small  Bunsen  flame. 
Allow  to  burn  quietly  until  the  flame  goes  out  and  then  use  the 
burner  to  keep  the  residue  red  hot. 
Shake  the  ash  into  the  crucible  and 
remove  the  last  portions  from  the 
wire  with  a  small  brush.  Finally 
transfer  any  portions  of  the  ash 
which  have  fallen  upon  the  glazed 
paper  into  the  crucible  and  heat  with 
the  free  flame  to  remove  the  last  trace 
of  carbonaceous  matter.  As  silver 
chloride  is  volatilized  at  a  compara- 
tively low  temperature  the  heating 
should  be  done  very  carefully.  Hold 
the  burner  in  the  hand  and  heat  only 
those  parts  of  the  crucible  which  show 
black  particles  of  carbonaceous  mat- 
ter. As  soon  as  the  carbon  is  all 
burned  remove  the  burner  at  once, 

allow  the  crucible  to  cool,  place  it  upon  a  sheet  of  glazed  paper, 
and  introduce  the  main  portion  of  the  precipitate.  Use  a  small 
brush  to  transfer  the  last  portion  of  the  precipitate  from  the 
glazed  paper  to  the  crucible. 

At  best  some  of  the  silver  chloride  precipitate  remaining  with 
the  filter  paper  has  been  reduced  to  silver,  and  this  must  be  changed 
to  silver  chloride  by  the  following  method.  Add  two  or  three 
drops  of  concentrated  nitric  acid  to  the  crucible,  warm,  and,  after 
allowing  to  cool  a  short  time,  add  one  or  two  drops  of  concentrated 
hydrochloric  acid.  The  contents  must  be  evaporated  to  complete 
dryness  without  loss  by  spattering.  This  is  best  accomplished  by 
placing  a  small  iron  pan  on  a  tripod,  and  supporting  the  crucible 
about  one  eighth  of  an  inch  above  the  bottom  of  the  pan  by 
means  of  a  triangle  resting  on  its  edges.  (See  Fig.  6.)  Place 


FIG.  6 


28  QUANTITATIVE  ANALYSIS 

under  the  pan  a  burner  which  is  so  regulated  that  it  will  not 
boil  the  contents  of  the  crucible.  When  the  contents  of  the 
crucible  have  evaporated,  holding  the  burner  in  the  hand,  heat 
it  with  the  small  free  flame  until  the  precipitate  just  begins  to 
fuse.  Cool  and  weigh.  Heat  again  and  weigh  as  described 
above,  until  the  weight  of  crucible  and  contents  is  constant. 

From  the  weight  of  the  precipitate,  calculate  the  weight  of 
chlorine  present  and  the  percentage  in  the  substance  taken -for 
analysis.  For  the  method  of  calculation  see  page  163. 

Notes. —  i.  The  presence  of  a  slight  excess  of  silver  nitrate  in 
the  solution  is  advantageous  because  of  the  fact  that  silver  chloride 
is  more  insoluble  in  water  containing  a  small  amount  of  silver 
nitrate ;  moreover,  it  helps  the  particles  of  the  precipitate  to 
become  coagulated. 

2.  Under  the  influence  of  light  the  silver  chloride  changes  from 
white  to  a  violet  color.     This  is  caused  by  a  part  of  the  precipitate 
changing  to  a  lower  chloride  with  the  loss  of  an  appreciable  amount 
of  chlorine.     The  chlorine  is  replaced,  however,  by  the  subsequent 
addition  of  nitric  and  hydrochloric  acids  to  the  precipitate. 

3.  Silver  chloride  is  almost  completely  insoluble  in  water  which 
contains  a  little  silver  nitrate.     It  is  very  slightly  soluble  in  cold 
water  and  in  cold  dilute  nitric  acid.     It  is  more  soluble  in  concen- 
trated nitric  acid ;  hence,  care  should  be  taken  that  the  precipita- 
tion does  not  take  place  in  a  solution  which  is  strongly  acid.     The 
precipitate  is  also  especially  soluble  in  concentrated  hydrochloric 
acid  and  hot  concentrated  solutions  of  chlorides. 

4.  Hot  water  dissolves  too  much  silver  chloride  to  permit  its  use 
in  washing  out  the  impurities.     Cold  water,  on  the  other  hand, 
causes   the  precipitate  to  return  to  the  colloidal   state  and  run 
through  the  filter.     This  is  prevented  by  adding  to  the  water  a 
small  amount  of  nitric  acid. 

5.  Silver    chloride  fuses   at    about    460°.      At   a   temperature 
slightly  higher  than  its  fusing  point  the  substance  begins  to  vola- 
tilize.   Considerable  care  should  be  exercised,  therefore,  in  heating 
this  substance. 

6.  The  fused  silver  chloride  may  be  removed  from  the  crucible 
by  placing  a  small  piece  of  zinc  upon  the  mass  and  adding  very 
dilute  hydrochloric   acid.     The  chloride  will  be  reduced  and  the 
metallic  silver  can  then  be  easily  removed. 


GRA  VIMETRIC  ANAL  YSIS  29 

7.  The  experiment  just  described  is  a  type  of  a  certain  class  of 
quantitative  determinations.     With  certain  modifications  bromine 
and  iodine  may  be  determined  by  this  method.     It  is  obvious, 
moreover,  that  the  method  may  be  reversed  and  that  a  metal  like 
silver  may  be  determined  by  the  addition  of  hydrochloric  acid  to 
a  solution  of  its  soluble  salt. 

8.  The  determination  of  the  chlorine  in  the  presence  of  a  heavy 
metal  is  complicated  by  the  fact  that  many  metals,  like  iron,  form 
basic  salts  under  the  condition  of  the  precipitation,  and  these  con- 
taminate the  precipitate.     In  such  cases  it  is  best  to  first  remove 
the  metal  by  means  of  a  suitable  precipitant. 

9.  The  filtrate  and  all  silver  residues  should  be  placed  into  the 
bottles  marked  "  Silver  Residues." 

REFERENCE 
FRESENIUS  (Cohn),  Vol.  I,  par.  82  b,  p.  198. 

EXERCISE  VI 
The  Determination  of  Sulphur  in  a  Soluble  Sulphate 

Procedure.  —  Obtain  the  substance  for  analysis  from  the  instructor 
and  weigh  two  portions  exactly  as  in  Exercise  V,  but  take  a  some- 
what larger  amount,  from  0.4  to  I  .o  gram  for  each  portion.  Dissolve 
in  100  c.c.  of  distilled  water,  and  acidify  with  2  or  3  c.c.  of  dilute 
hydrochloric  acid.  Heat  the  solution  to  boiling  and  add,  drop  by 
drop,  at  a  rate  not  exceeding  5  c.c.  per  minute,  about  ro.c.c.  of  a  hot 
solution  of  barium  chloride.  The  barium  chloride  is  best  added  by 
means  of  a  small  medicine  dropper  similar  to  those  used  for  filling 
fountain  pens.  Be  sure  that  an  excess  of  the  precipitating  reagent 
has  been  added  to  the  solution.  Keep  the  solution  at  a  temperature 
near  the  boiling  point  for  about  an  hour,  then  allow  the'precipitate 
to  settle. 

Prepare  two  filters  in  the  usual  way.  If  the  precipitates  have 
been  properly  digested,  and  a  good  grade  of  filter  paper  is  used,  no 
trouble  should  be  caused  by  the  particles  running  through  the 
filter.  As  an  extra  precaution  double  filters  may  be  used  or  a  sin- 
gle filter  may  be  saturated  with  a  hot  concentrated  solution  of 
ammonium  chloride.  Decant  the  hot  supernatant  liquid  upon  the 
filter.  Watch  the  filtrate  closely,  and  if  it  is  turbid,  replace  the 
beaker  containing  the  filtrate  with  a  clean  one,  and  pass  the  filtrate 


QUANTITATIVE  ANALYSIS 


through  the  filter  again.  Do  not  proceed  with  the  filtration  until 
a  clear  filtrate  is  obtained.  Wash  the  precipitate  three  or  four 
times  by  decantation,  using  hot  water  containing  a  little  hydrochloric 
acid.  Replace  the  beaker  containing  the  filtrate  by  a  clean  one, 
transfer  the  precipitate  to  the  filter  as  in  the  determination  of  chlo- 
rine, and  wash  with  hot  water  from  the  wash  bottle  until  3  c.c.  of 
the  filtrate  give  no  test  for  chlorides.  Place  the  funnel  and  con- 
tents into  the  drying  closet. 

When  dry,  remove  the  filter  from  the  funnel  and  fold  it  in  such 
a  way  that  it  can  be  placed  into  a  previously  weighed  porcelain 

crucible.  Be  sure  that 
the  part  of  the  filter 
paper  containing  the 
main  portion  of  the 
precipitate  is  placed 
in  the  bottom  of  the 
crucible.  If  any  of 
the  precipitate  has 
crept  over  the  edge  of 
the  filter  and  adheres 
to  the  funnel,  remove 

FlG  7  it  by  means  of  a  piece 

of  moist  ashless  filter 

paper  and  place  this  into  the  crucible  with  the  filter.  Place  the 
crucible  in  a  reclining  position  on  the  triangle,  and  only  partially 
cover  with  the  crucible  cover  so  that  a  current  of  air  will  pass 
over  the  filter.  (See  Fig.  7.) 

Place  the  burner  under  the  crucible  and  heat  gently  with  a  low 
flame  until  volatile  matter  begins  to  come  off.  Do  not  allow 
the  volatile  gases  to  take  fire,  as  this  is  attended  by  mechanical 
loss  of  the  barium  sulphate.  If  this  should  happen,  extinguish 
the  flame  by  means  of  the  crucible  cover.  Gradually  increase  the 
flame  until  the  volatile  matter  is  expelled  and  nothing  but  a  little 
carbonaceous  matter  is  left  with  the  precipitate.  Heat  to  the  full 
heat  of  the  burner,  directing  the  flame  toward  the  base  of  the 
crucible.  When  the  carbon  is  all  oxidized,  cool  the  crucible  in  the 
desiccator  and  weigh.  Heat  again  and  repeat  until  constant 
weight  is  obtained.  From  the  weight  of  barium  sulphate  calculate 
the  percentages  of  sulphuric  anhydride  and  of  sulphur  present  in 
the  original  sample.  For  the  method  of  calculation  see  page  165. 


GRA  VIMETRIC  ANAL  YSIS  3 1 

Notes. —  i.  The  precipitate  of  barium  sulphate  possesses  to  a 
marked  degree  the  power  of  dragging  down  or  occluding  other 
substances  which  cannot  be  easily  removed  by  wash  water.  This 
may  result  in  either  high  or  low  results.  In  the  presence  of  iron, 
aluminium,  or  chromium  the  precipitate  may  be  contaminated  with 
the  sulphates  of  these  metals.  On  ignition,  sulphur  trioxide  is 
given  off,  and  the  results  obtained  are  low.  In  the  presence  of 
potassium  salts  low  results  are  obtained  owing  to  the  fact  that  the 
precipitate  is  contaminated  with  potassium  sulphate. 

When  nitrates  or  chlorates  are  present,  the  precipitate  will  con- 
tain the  barium  salts  of  these  acids,  consequently  high  results  will 
be  obtained.  The  rapid  addition  of  the  precipitating  reagent  gives 
high  results  due  to  the  occlusion  of  barium  chloride.  In  general, 
the  amount  of  occlusion  is  greater  in  concentrated  solutions. 

From  the  above  it  is  obvious  that  the  solution  from  which  the 
sulphate  is  to  be  precipitated  must  be  as  free  as  possible  from  iron, 
aluminium,  chromium,  and  potassium  salts.  Moreover,  nitric  and 
chloric  acids  must  be  absent. 

2.  The  addition  of  an  excess  of  hydrochloric  acid  is  to  be  avoided. 
Not  only  does  it  tend  to  dissolve  the  precipitate,  but,  as  has  been 
shown  by  Richards,  it  also  increases  the  amount  of  barium  chloride 
occluded. 

3.  If  precipitated  in  a  cold  or  very  dilute  solution,  barium  sul- 
phate will  be  found  to  be  present  in  a  very  finely  divided ,  state 
unless  allowed  to  stand  for  several  hours.     If   precipitated  in  a 
boiling  solution,  and  then  heated,  the  particles  are  larger.     (See 
page  n.) 

4.  The  precipitate  may  be  considered  as  insoluble  in  water  and 
dilute  acids.     It  is  appreciably  soluble,  however,  in  concentrated 
hydrochloric  acid  and  more  soluble  in  either  concentrated  nitric 
or  sulphuric  acids.     The  presence  of  either  a  soluble  barium  salt 
or  a  soluble  sulphate  decreases  the  solubility  of  the  barium  sul- 
phate.    In   this   determination,  therefore,  a  small  excess  of   the 
precipitating  reagent  is  advantageous.     (See  page  n.) 

5.  The  filter  containing  the  barium  sulphate  may  also  be  ignited 
without  first  drying.  f  In  this  case  extreme  care  must  be  used  to 
heat  slowly.     The  filter  should  be  placed  into  the  crucible,  which  is 
inclined  on  a  triangle,  as  described  above,  and  heated  with  a  low 
flame  which  is  directed  towards  the  top  of  the  crucible.     This  dries 
the  precipitate  from  the  top  downwards,  so  that  there  is  no  danger 


32  QUANTITATIVE  ANALYSIS 

of  particles  being  blown  out  of  the  crucible  by  the  sudden  forma- 
tion of  steam.  The  final  ignition  is  conducted  in  the  manner 
already  described. 

6.  If  the  precipitate  is  ignited  slowly,  the  filter  is  easily  oxidized. 
Rapid  heating  changes  it  to  a  form  of  carbon  resembling  graphite, 
which  is  oxidized  with  extreme  difficulty. 

7.  By  reversing  this  determination  it  is  apparent  that  barium 
may  be  estimated  as  the  sulphate.     This  is  true  of  strontium  ;   and, 
with  certain  modifications  of  the  method,  lead  may  also  be  deter- 
mined in  this  way. 

REFERENCES 

FOLIN,  Journal  of  Biological  Chemistry,  1,   131  (1906). 

HULETT  AND  DusCHAK,  Zeitschrift  fur  anorganische  Chemie,  40,  196  (1904). 
RICHARDS  AND  PARKER,  Proceedings  of  the  American  Academy  of  Arts  and 
Sciences,  23,  67  (1895). 


EXERCISE  VII 

Separation   and  Determination  of  Calcium  and  Magnesium  in  a 
Mixture  of  their  Carbonates 

Calcium 

Procedure. — Weigh  out  two  portions  of  the  sample  of  about 
i  gram  each  into  No.  3  beakers,  add  about  10  c.c.  of  water  and 
cover  with  cover-glasses.  By  means  of  a  stirring  rod  introduce 
through  the  opening  between  the  lip  of  the  beaker  and  the  cover- 
glass  about  20  c.c.  of  dilute  hydrochloric  acid.  Heat  the  beaker 
on  an  asbestos  gauze,  and  if  any  of  the  substance  remains  undis- 
solved,  add  more  acid  and  warm  again.  Continue  heating  until  all 
of  the  carbon  dioxide  gas  is  expelled ;  wash  the  cover-glass  with  a 
little  water  in  order  to  recover  any  of  the  solution  that  may  have 
spattered  upon  it.  Dilute  the  solution  to  approximately  200  c.c., 
make  alkaline  with  ammonium  hydroxide,  and  heat  to  boiling.  To 
the  hot  solution  add  slowly  25  c.c.  of  a  freshly  prepared  solution 
of  ammonium  oxalate,  stirring  well.  Digest  at  a  temperature  near 
the  boiling  point  for  an  hour,  allow  the  precipitated  calcium  oxalate 
to  settle,  and  decant  the  supernatant  liquid  through  a  filter,  keep- 
ing as  much  of  the  precipitate  as  possible  in  the  beaker.  Wash 
the  precipitate  three  times  by  decantation,  using  20  c.c.  of  hot 
water  each  time.  Test  the  filtrate  for  complete  precipitation  by 


GRA  VIMETRIC  ANAL  YSIS  3 3 

adding  a  few  drops  of  the  ammonium  oxalate  solution  and  allowing 
to  stand.  If  no  precipitate  forms,  make  the  nitrate  slightly  acid 
and  evaporate  it  on  the  steam  bath  for  the  determination  of 
magnesium. 

Place  the  beaker  containing  the  calcium  oxalate  precipitate  un- 
der the  funnel,  and  dissolve  the  calcium  oxalate  by  pouring  suc- 
cessive portions  of  warm  dilute  hydrochloric  acid  through  the 
filter,  washing  the  filter  this  way  three  times.  When  the  calcium 
oxalate  is  all  dissolved,  finally  wash  the  filter  with  dilute  ammonium 
hydroxide  solution.  Dilute  the  solution  to  about  200  c.c.,  add  am- 
monium hydroxide  in  slight  excess,  then  add  5  c.c.  of  the  ammo- 
nium oxalate  solution,  and  digest  as  before  for  about  an  hour. 
Filter  the  calcium  oxalate  upon  the  filter  which  was  first  used  and 
wash  the  precipitate  with  hot  water  until  it  is  free  from  chlorides. 
Add  the  first  three  washings  to  the  filtrate,  then  use  another 
beaker  to  collect  the  remainder  of  the  washings.  The  filtrate 
should  be  made  just  slightly  acid  with  hydrochloric  acid,  com- 
bined with  the  first  filtrate,  and  used  for  the  determination  of  mag- 
nesium. (See  below.) 

Dry  the  precipitate  of  calcium  oxalate  in  the  drying  closet  and 
ignite  as  described  in  the  determination  of  sulphur.  By  heating, 
the  calcium  oxalate  is  changed  first  to  calcium  carbonate  and 
finally  to  calcium  oxide.  Allow  the  crucible  to  cool,  and  very 
carefully  moisten  the  residue  in  the  crucible  after  the  carbon  has 
all  been  consumed,  first  with  one  cubic  centimeter  of  water,  then 
with  a  few  drops  of  dilute  sulphuric  acid.  Heat  very  cautiously  to 
evaporate  the  excess  of  acid.  When  the  white  fumes  cease  to  be 
given  off  from  the  crucible,  add  a  few  drops  more  of  the  sulphuric 
acid  and  evaporate  to  dryness.  Heat  to  redness  by  means  of  the 
free  flame,  cool,  and  weigh.  Repeat  the  treatment  with  sulphuric 
acid  until  the  weight  is  constant.  All  of  the  calcium  is  thus  con- 
verted into  calcium  sulphate,  in  which  form  it  is  weighed.  From 
the  weight  of  the  calcium  sulphate  calculate  the  weight  of  calcium 
oxide  and  the  percentage  present  in  the  substance  taken  for 
analysis. 

Magnesium 

Concentrate  the  slightly  acidified  filtrate  from  the  calcium  deter- 
mination by  heating  on  the  water  bath.  When  the  volume  is 
about  200  c.c.,  cool,  add  ammonium  hydroxide  until  it  is  just  neu- 

D 


34  QUANTITATIVE  ANALYSIS 

tral,  or  only  very  faintly  alkaline.  Add  drop  by  drop  1 5  c.c.  of  a 
solution  of  sodium  ammonium  hydrogen  phosphate  (microcosmic 
salt).  Add  slowly  to  the  solution  one  third  its  volume  of  ammo- 
nium hydroxide  (sp.  gr.  0.96)  with  constant  stirring.  Allow  the 
solution  to  stand  for  several  hours,  then  decant  the  supernatant 
liquid  through  a  filter  and  wash  the  precipitate  three  times  by 
decantation,  using  2\  per  cent  ammonia  solution  and  leaving  as 
much  of  the  precipitate  as  possible  in  the  beaker.  [Calculate  the 
amount  of  desk  reagent  required  to  make  500  c.c.  of  the  2\  per 
cent  ammonia  solution  and  dilute  this  quantity  to  the  required 
volume.]  Dissolve  the  precipitate  on  the  filter  by  pouring  small 
quantities  of  warm  hydrochloric  acid  through  the  filter,  receiving 
the  filtrate  in  the  beaker  in  which  the  precipitation  of  the  magne- 
sium ammonium  phosphate  took  place.  Wash  the  filter  three 
times  with  warm,  slightly  acid  water.  Dilute  the  solution  to  about 
200  c.c.,  and  add  ammonium  hydroxide  drop  by  drop  until  the 
solution  is  slightly  alkaline,  stirring  vigorously  meanwhile.  Now 
add  a  few  drops  of  the  microcosmic  salt  solution  to  insure  com- 
plete precipitation.  Then  add  one  third  the  volume  of  ammonium 
hydroxide  with  constant  stirring,  and  allow  to  stand  for  several 
hours.  Decant  the  supernatant  liquid  through  a  filter,  wash  the 
precipitate  three  times  by  decantation,  using  cold  2\  per  cent 
ammonia  solution,  then  transfer  the  precipitate  to  the  filter,  con- 
tinuing the  washing  with  the  dilute  ammonium  hydroxide  until  a 
few  cubic  centimeters  of  the  filtrate  give  no  test  for  chlorides.  Dry 
the  precipitate,  transfer  the  main  bulk  to  a  glazed  paper,  and  burn 
the  filter  separate  from  the  precipitate  as  directed  in  the  determi- 
nation of  chlorine,  but  omit  the  treatment  with  acids.  Transfer 
the  precipitate  to  the  crucible,  bring  gradually  to  the  full  heat  of 
the  Bunsen  flame,  and  heat  until  the  precipitate  is  white.  Cool 
in  the  desiccator,  weigh,  and  heat  to  constant  weight.  From  the 
weight  of  the  pyrophosphate  calculate  the  weight  of  magnesium 
oxide,  and  the  percentage  of  magnesium  oxide  in  the  substance 
taken  for  analysis. 

Notes.  —  i.  The  separation  of  calcium  and  magnesium  depends 
upon  the  different  solubilities  of  the  two  oxalates.  Calcium  oxa- 
late  is  practically  insoluble  in  hot  water,  whereas  magnesium 
oxalate  is  relatively  soluble.  Magnesium  oxalate  is,  however, 
much  more  soluble  in  water  containing  an  excess  of  ammonium 


GRAVIMETRIC  ANALYSIS  35 

salts.  If  a  large  amount  of  magnesium  is  present,  the  precipitate 
of  calcium  will  contain  some  magnesium  oxalate,  and  a  reprecipita- 
tion  is  necessary. 

2.  The  solution  should  be  well  boiled  to  expel  the  carbon  diox- 
ide.    If  this  is  not  entirely  removed,  on  adding  ammonium  hy- 
droxide  and   ammonium    oxalate   the   precipitate  will    consist   of 
calcium  oxalate  and  calcium  carbonate.     As  this  latter  compound 
is  more  soluble  than  the  oxalate,  it  is  well  to  avoid  its  formation. 

Ammonium  oxalate  solution  should  be  freshly  prepared.  On 
standing  it  undergoes  decomposition,  ammonium  carbonate  being 
one  of  the  products  formed. 

3.  Calcium  oxalate  on  gentle  ignition  below  visible  redness  is 
changed  to  the  carbonate  and  as  such  may  be  weighed.     A  tem- 
perature slightly  too  high,  however,  expels  some  carbon  dioxide. 
The  complete  conversion  to  the  oxide  requires  heating  in  a  plati- 
num crucible  at  a  high  temperature.     The  action  of  the  sulphuric 
acid  on  the  calcium  oxalate,  oxide,  and  carbonate  is  to  convert  them 
into  calcium  sulphate.     This  compound  will  stand  the  cherry  red 
heat  of  a  Bunsen  burner  without  alteration ;  the  higher  heat  of  the 
blast  will  cause  it  to  lose  sulphuric  anhydride. 

4.  On  concentrating  the  filtrate  from  the  calcium   oxalate,   a 
crystalline  precipitate  of  magnesium  oxalate  will  sometimes  settle 
out.     This  may  be  dissolved  in  dilute  hydrochloric  acid  and  added 
to  the  solution. 

5.  The    complete    precipitation    of    magnesium    as    the    salt 
MgNH4PO4   takes    place    only   under   certain   conditions   which 
must  be  closely  observed. 

Contamination  of  the  precipitate  may  occur : l 

a.  When  the  precipitation  takes  place  in  a  strongly  ammoniacal 
solution,  particularly  when  the  phosphate  is  slowly  added,  the  pre- 
cipitate under  these  conditions  always  contains  some  of  the  normal 
magnesium  phosphate. 

b.  If  the  precipitation  takes  place  in  a  neutral  or  slightly  am- 
moniacal solution  in  the  presence  of  ammonium  salts  and  ammo- 
nium hydroxide  is  afterwards  added,  the  precipitate  then  always 
contains  some  magnesium  tetra  ammonium  phosphate. 

To  insure  a  pure  precipitate,  the  solution  must  -be  neutral,  as 

1  This  discussion  of  the  determination  of  magnesium  follows  very  closely  Treadwell's 
(Treadwell-Hall,  Vol.  II,  p.  62,  ed.  1904)  description  of  the  experiments  of  Neubauer 
(Zeit.  fur  Angew.  Chem.  p.  439,  1896). 


36  QUANTITATIVE  ANALYSIS 

free  as  possible  from  ammonium  salts,  and  the  ammonium  hydrox- 
ide must  be  added  after  the  addition  of  microcosmic  salt  solution. 

6.  The  solution  in  which  precipitation  takes  place  may  be  freed 
from  ammonium  salts : 

a.  By  evaporation  of  the  solution  and  the  ignition  of  the  resi- 
due, or  evaporation  to  dryness  with  an  excess  of  nitric  acid. 

b.  By  first  precipitating  the  magnesium  in  the  presence  of  the 
ammonium  salts,  then  dissolving  the  impure  precipitate  in  a  small 
amount  of    acid,  and  reprecipitating.     The    second   precipitation 
takes  place  under  the  specified  conditions,  and  the  precipitate  is 
obtained  pure. 

7.  On  the  addition  of  a  microcosmic  salt  solution  to  the  neutral 
solution   containing   magnesium,   90   per    cent  of  the  magnesium 
present  is  at  once  precipitated  as  magnesium  hydrogen  phosphate 
(MgHPO4).     When  ammonium  hydroxide  is  added   to   the   cold 
solution,  this  precipitate  is  changed  to  the  crystalline  magnesium 
ammonium -phosphate.   •  The  10  per  cent  of  the  magnesium  hydro- 
gen phosphate  which  remained  in  the  solution  is  also  completely 
precipitated   by  this  procedure   as  magnesium   ammonium  phos- 
phate. 

8.  Magnesium  ammonium  phosphate  is  appreciably  soluble  in 
hot  water,  but  is  much  less  soluble  in  cold  water.     It  is  least  solu- 
ble in  a  cold  dilute  solution  of  ammonium  hydroxide. 

9.  During  ignition  the  magnesium  ammonium  phosphate  loses 
water  and  ammonia,  and  is  converted  into  magnesium  pyrophos- 
phate.     If  the  pyrophosphate  appears  gray,  it  may  be  whitened 
by  moistening  with  a  few  drops  of  concentrated  nitric  acid  and 
reigniting  after  expulsion  of  the  excess  of  nitric  acid  by  heating 
over  a  radiator. 

REFERENCES 

Calcium 
FRESENIUS,  Quantitative  Analysis  (Cohn),  Vol.  I,  par.  73,  p.  173. 

Magnesium 

W.  F.  HILLEBRAND,  The  Analysis  of  Silicate  and  Carbonate  Rocks,  Bull.  No. 

305,  U.S.  Geol.  Surv.,  p.  105. 
FRESENIUS,  Quantitative  Analysis  (Cohn),  Vol.  I,  par.  74,  p.  176. 


GRAVIMETRIC  ANALYSIS 


37 


EXERCISE  VIII 
The  Determination  of  Aluminium  in  a  Soluble  Salt 

Procedure.  —  Obtain  a  sample  containing  aluminium  and  weigh 
out  two  portions  of  about  one  gram  each.  Dissolve  in  100  c.c.  of 
hot  water,  add  about  5  c.c.  of  concentrated  hydrochloric  acid,  and 
then  enough  of  a  clear  solution  of  ammonium  hydroxide  to  make 
the  solution  slightly  alkaline.  Test  with  litmus  paper  or  by  odor 
after  stirring  thoroughly.  Be  sure  to  avoid  adding  more  than  a 
slight  excess  of  ammonium  hydroxide.  Boil  gently  until  the  liquid 
gives  only  a  very  slight  odor  of  ammonia,  or  shows  a  slightly 
alkaline  reaction.  Allow  the  precipitate  to  settle,  then  filter  at 
once. 

This  nitration  can  best  be  accomplished  by  the  use  of  suction. 
Obtain  from  the  supply  room  the  apparatus  to  be  used  for  this 
purpose,  which  consists  of  the  following : 
i  filter  pump  ; 

1  glass  T-tube; 

2  filter  flasks  (500  c.c.); 

2  rubber  stoppers  (i  hole)  to  fit  the  flasks; 

2  hardened  filter  cones ; 

2  ashless  filter  papers,  1 1  cm. 

Attach  the  filter  pump  to  a  water  cock.  Connect  to  this,  by  means 
of  rubber  tubing  and  the  glass  T-tube,  the  two  filter  flasks  which 
carry  by  means  of  the  rubber  stoppers  the  two  funnels.  Fold  the 
half  form  hardened  filter  into  a  cone  by  the  method  shown  in  Fig. 
8,  and  place  into  the  funnels.  Upon  these  place  the  1 1  cm.  filter 


FIG 


papers  folded  in  the  usual  way.  Press  the  papers  into  position, 
be  sure  that  the  filter  paper  fits  the  funnel  snugly  at  the  upper 
edge,  and  moisten  with  a  little  distilled  water. 

Pour  the  clear  supernatant  liquid  through  the  filter  and  wash 


38  QUANTITATIVE  ANALYSIS 

the  precipitate  by  decantation,  using  boiling  water  which  contains 
a  few  drops  of  ammonium  hydroxide  and  two  or  three  grams  of 
ammonium  nitrate  per  liter.  Use  a  gentle  suction  to  accelerate 
the  filtration  and  always  keep  some  liquid  in  the  funnel  while  suc- 
tion is  being  employed.  Finally,  transfer  the  precipitate  to  the 
filter,  wash  free  from  chlorides,  dry  the  filter,  and  ignite  as  in  the 
determination  of  sulphur.  After  burning  the  carbon  of  the  filter, 
heat  the  precipitate  in  the  flame  of  a  blast  lamp  until  the  weight 
is  constant.  Calculate  the  percentage  of  aluminium  oxide  present 
in  the  sample  taken  for  analysis. 

Notes.  —  I.  The  complete  precipitation  of  aluminium  as  the 
hydroxide  takes  place  only  in  the  presence  of  certain  salts,  in 
this  case  ammonium  salts.  The  ammonium  salts  have  a  twofold 
function,  they  decrease  the  tendency  of  the  excess  of  ammonium 
hydroxide  to  dissolve  the  precipitate,  and  they  also  prevent  the 
aluminium  hydroxide  from  running  through  the  filter  in  a  colloidal 
or  semisoluble  condition.  The  presence  of  the  ammonium  nitrate 
in  the  wash  water  has  a  similar  effect. 

2.  Prolonged  boiling  to  expel  the  excess  of  ammonia  should  be 
avoided,  as  it  may  result  in  the  solution  becoming  acid,  with  the 
subsequent  dissolving  of  a  part  of  the  precipitate. 

3.  The  aluminium  hydroxide  should  be  filtered  as  soon  as  pos- 
sible after  precipitation.     On  standing,  it  adheres  to  the  beaker 
and  is  removed  only  with  great  difficulty. 

4.  The  precipitate  should  not  be  allowed  to  stand  in  the  funnel 
for  any  great  length  of   time  without  washing,  as   it  dries  and 
cracks,  and  is  then  almost  impossible  to  wash  free  from  impurities. 
The  washing  should  be  continued  until  all  chlorides  are  removed, 
as   any   ammonium   chloride  not  washed   out  will   form  volatile 
aluminium  chloride  on  igniting  the  precipitate. 

5.  When  aluminium   hydroxide  is  ignited,  water  is  given  off 
with  the  formation    of  AIO(OH),   and   on   further   ignition  alu- 
minium oxide  is  formed.     The  aluminium  oxide  parts  with  the  last 
trace  of  water  with  difficulty,  so  that  the  final  heating  must  be 
done  with  the  blast  lamp.     As  the  aluminium  oxide  also  absorbs 
water  easily,  unless  it  is  weighed  quickly  a  considerable  amount 
of  water  will  be  taken  up.     The  weighing  is  best  accomplished  by 
obtaining  an  approximate  weight  of  the  crucible  plus  the  precipi- 
tate, then  making  a  second  weighing  by  placing  the  necessary 


GRA  VIMETRIC  ANAL YSIS  39 

weights  upon  the  pan,  removing  the  crucible  from  the  desiccator 
and  completing  the  weighing  by  means  of  the  rider. 

6.  Many  other  metals,  such  as  iron,  chromium,  nickel,  and  cop- 
per are  determined  by  precipitating  as  the  hydroxide  in  a  manner 
similar  to  that  just  described.  With  the  last  two  metals,  potassium 
hydroxide  is  usually  employed  as  the  precipitating  reagent. 

REFERENCE 
FRESENIUS,  Quantitative  Analysis  (Cohn),  Vol.  I,  par.  75,  p.  179. 


PART    III 

VOLUMETRIC   ANALYSIS 

VOLUMETRIC  analysis  comprises  those  methods  wherein  the  con- 
stituent of  a  sample  is  not  isolated  and  weighed,  but  determined  by 
allowing  a  solution  of  known  composition  to  react  with  it,  either 
directly  or  indirectly.  From  the  volume  of  the  solution  used,  the 
amount  of  the  constituent  can  be  computed  by  means  of  the  laws 
of  chemical  equivalents.  For  example,  in  a  solution  containing 
sodium  chloride,  the  amount  present  can  be  determined  by  pre- 
cipitating the  chlorine  as  silver  chloride,  by  the  addition  of  a  solu- 
tion of  silver  nitrate  of  known  strength.  In  order  to  indicate  the 
point  at  which  all  of  the  chlorine  is  precipitated,  a  little  potassium 
chromate  is  added  to  the  solution.  When  the  silver  nitrate  has  pre- 
cipitated all  of  the  chlorine  as  silver  chloride,  the  next  drop  of  the 
solution  added  will  react  with  the  potassium  chromate  with  the  for- 
mation of  a  permanent  reddish  precipitate  of  the  chromate  of  silver. 
A  substance,  such  as  potassium  chromate,  which  is  used  to  show 
when  a  reaction  is  complete  is  called  an  Indicator.  It  is  very  easy 
to  detect  this  point  at  which  all  of  the  chlorine  is  precipitated,  and 
from  the  amount  of  silver  nitrate  solution  added  the  equivalent 
quantity  of  chlorine  can  be  readily  calculated. 

VOLUMETRIC   APPARATUS1 

The  ordinary  methods  of  volumetric  analysis  require  the  employ- 
ment of  vessels  which  will  contain  or  deliver  definite  specified 
quantities  of  solutions.  The  vessels  in  general  use  are  the  follow- 
ing: 

Pipettes  are  used  to  deliver  definite  amounts  of  liquids.  They 
are  of  two  general  kinds  :  Those  provided  with  one  mark  deliver 
but  one  specified  quantity  of  liquid.  This  form  is  illustrated  by  the 

1  See  report  of  the  committee  for  cooperation  with  the  National  Bureau  of  Standards, 
Jour.  Am.  Chem.  Soc.  Proceedings,  p.  17  (1904). 

40 


VOLUMETRIC  ANALYSIS 


c.c. 


40 


•=-20 


25  c.c.  pipette  in  Fig.  9.  Those  with  two  marks  have  the  interven- 
ing space  subdivided  and  permit  the  exact  measurement  of  different 
quantities  of  liquid.  This  form  is  represented  by  the  10  c.c. 
pipette  in  Fig.  9.  To  fill  the  pipette  the  liquid  is 
sucked  above  the  upper  mark  and  is  then  held  in 
place  by  placing  the  index  finger  over  the  top.  The 
liquid  is  lowered  to  the  mark  by  slowly  rotating  the 
pipette  between  the  thumb  and  middle  finger,  and  is 
allowed  to  run  out  into  the  desired  vessel  by  raising 
the  index  finger.  The  opening  through  which  the 
liquid  is  delivered  should  be  small,  since  the  speed  of 
outflow  determines  the  amount  of  liquid  remaining  on 
the  inner  surface.  In  order  to  re- 
move a  constant  quantity  of  liquid, 
hold  the  point  against  the  wall 
of  the  receiving  vessel  during 
the  free  outflow  and  for  fifteen 
seconds  thereafter. 

Graduated  Cylinders  are  of  vari- 
ous sizes,  ranging  from  a  few  cubic 
centimeters  to  a  liter  or  more  in 
capacity.  They  are  usually  not 
graduated  in  small  divisions  and 
are,  therefore,  employed  when 
liquids  are  to  be  measured  only 
roughly.  The  usual  form  is  rep- 
resented in  Fig.  10. 

Graduated  Flasks  are  made  in 
sizes  ranging  from  25  c.c.  to 
several  liters  in  capacity.  The 
general  form  is  illustrated  in  Fig. 
ii.  They  are  usually  provided 
with  two  marks,  the  lower  one  in- 
dicating the  point  to  which  the  flask  is  to  be 
filled  in  order  to  have  contained  therein  the  des- 
ignated amount,  while  the  upper  mark  indicates  the  amount  which 
should  be  placed  into  the  flask  in  order  to  remove  from  it  the 
specified  quantity,  the  difference  in  the  two  quantities  being  the 
amount  of  the  liquid  that  will  adhere  to  the  inner  surface  of 
the  flask. 


FIG.  9 


FIG.  10 


OF  THE 

UNIVERSITY 


QUANTITATIVE  ANALYSIS 


(_) 


Burettes  are  long  tubes  graduated  in  cubic  centimeters  and  frac- 
tions thereof,  from  which  liquids  may  be  conveniently  measured. 
They  have  capacities  ranging  as  high  as  100  c.c.  In  the  authors' 
laboratories  burettes  of  30  c.c.  capacity  graduated  to  ^V  °f  a  cu°ic 
centimeter  have  been  found  to  be  of  convenient  size.  Two  such 
burettes  with  a  burette  holder  are  represented  in  Fig.  12.  Burettes 

should  be  read  to  hundredths  of  a  cubic  centi- 

meter,  and  in  reading  them  the  exact  position  of 

the  curved  surface  of  the  liquid,  termed  the  me- 

niscus, will  depend  upon  the  position  of  the  eye. 

Hence,  great   care  should 

be  exercised   to   have  the 

eye   on    a   level   with    the 

meniscus.     Many    devices 

are  employed  to  facilitate 

reading     burettes.       That 

represented   in    Fig.    13 

shows    a    strip    of    paper 

wrapped    around    the   bu- 

rette by  means    of  which 

the  position  of  the  menis- 

cus can  be   accurately  lo- 

cated.    The  paper  should 

be  held  in  such  a  position 
that  the  upper  edge  will  be  about  one  milli- 
meter below  the  lower  surface  of  the  menis- 
cus, and  the  eye  on  a  level  with  the  two 
upper  edges  of  the  paper.  Parallax  can 
also  be  avoided  by  providing  burettes  with 
marks  which  extend  nearly  or  quite  around 
them.  A  method  of  having  burettes  con- 
structed with  a  white  back  in  the  center  of 
which  is  a  blue  stripe,  has  been  devised  by 
Shellbach.  By  this  arrangement  the  menis- 
cus appears  to  be  divided  -into  two  parts 
which  meet  in  a  point  in  the  center,  thus 
giving  a  sharp  definite  point,  which  is  very  accurately  located. 


FIG.  ii 


mcolnsBuretteHo 


•MH 


FIG.  13 


VOLUMETRIC  ANALYSIS 


43 


THE   CALIBRATION   OF  GRADUATED   APPARATUS 

In  accurate  chemical  work  the  capacity  of  all  graduated  apparatus 
should  be  carefully  tested.  This  process  of  testing  is  known  as 
Calibration.  The  vessels  to  be  used  should  all  be  calibrated  among 
themselves,  so  that  the  relation  is  accurately  known.  The  25  c.c. 
pipette  should  deliver  exactly  the  same  amount  of  a  solution  as  is 
delivered  by  the  burette  when  it  reads  25  c.c.,  and  this  quantity 
should  be  -^  the  amount  contained  in  the  250  c.c.  flask,  and  -fa  the 
capacity  of  the  1000  c.c.  flask.  It  does  not  make  any  difference  at 
what  temperature  these  vessels  are  calibrated,  because  the  meas- 
urements are  only  relative.  Nor  does  it  make  any  difference  what 
unit  is  employed,  provided  the  same  one  is 
used  for  all  of  the  different  measuring  vessels. 
The  Mohr  cubic  centimeter  has  been  used  ex- 
tensively as  the  unit  of  volume  in  volumetric 
work  and  is  defined  as  the  volume  of  one  gram 
of  water  at  17.5°  weighed  in  air  with  brass 
weights.  This  is  not,  however,  a  true  cubic 
centimeter,  which  is  defined  as  the  volume  of 
one  gram  of  water  in  vacuum  at  its  greatest 
density  (4°  C).  The  relation  between  the 
Mohr  cubic  centimeter  and  the  true  cubic 
centimeter  is 


i   Mohr  c.c.  =  1.0023  true  c.c. 


17 


18 


20 


In  other  words,  1000  grams  of  water,  weighed 
in  air,  would  occupy  a  volume  of  1002.3  c.c.  at 
17.5°,  or  the  Mohr  liter  would  occupy  a  greater 
volume  than  the  true  liter. 

For  the  most  accurate  work,  in  which  solutions  of  definite  con- 
centrations are  to  be  prepared,  also  for  the  calibration  of 
burettes  for  measuring  gases,  the  true  cubic  centimeter  should 
be  used  as  the  standard  of  calibration. 

Suppose  we  desire  to  calibrate  a  liter  flask  in  true  cubic  centi- 
meters. The  dry  flask  is  placed  upon  the  balance  pan  and  suffi- 
cient weights  are  added  to  counterpoise  it.  Now,  as  we  desire  to 
establish  a  mark  on  the  flask  which  represents  just  one  liter  or  1000 
true  cubic  centimeters  which  weigh  1000  grams  in  vacuum,  the 


44  QUANTITATIVE  ANALYSIS 

question  arises  what  difference  would  there  be  between  the  weight 
in  air  and  in  vacuum  ?  How  much  weight  shall  be  placed  upon 
the  pan  to  represent  the  1000  grams  of  water  in  vacuum  ?  One 
kilogram  of  water  displaces  approximately  one  liter  of  air,  which 
under  the  ordinary  conditions  of  temperature  and  pressure  weighs 
about  1.2  grams.  (One  literate0  under  a  pressure  of  one  atmos- 
phere weighs  1.293  grams.)  Just  as  the  weight  of  a  body  in  a 
liquid  is  lighter  than  its  weight  in  air  by  the  amount  of  the  liquid 
displaced,  so  the  water  is  lighter  in  air  than  in  a  vacuum  by  the 
weight  of  the  air  it  displaces.  Therefore,  one  liter  of  water  is 
lighter  by  1.2  grams  when  weighed  in  air  than  when  weighed  in 
vacuum.  But  the  brass  weights  with  which  it  is  weighed  are  also 
lighter  than  they  would  be  were  they  weighed  in  vacuum  ;  hence, 
since  brass  has  a  specific  gravity  of  8.4  (i.e.,  8.4  times  as  heavy 
as  an  equal  volume  of  water),  a  kilogram  of  brass  weights  would 

occupy  only   -  — ,  or  —  of  the  volume  of  the  water.     These  brass 
8.4         84 

weights   would   displace   —   of    1.2,    or  0.14  gram  of  air.      The 

84 

weight  of  the  kilogram  of  water  in  air  is  then  decreased  1.2  grams 
and  that  of  the  kilogram  of  brass  weights,  0.14  gram  ;  hence,  the 
total  decrease  of  the  weight  of  water  due  to  the  buoyant  action  of 
air  will  be  the  difference  between  1.2  and  0.14,  or  1.06  grams.  A 
kilogram  of  water,  i.e.,  exactly  1000  grams,  weighed  in  vacuum, 
will  weigh  in  air  with  brass  weights  1000—  1.06,  or  998.94  grams, 
and  will  occupy  at  4°  C.,  1000  true  cubic  centimeters,  or  one  liter. 
But  let  us  assume  we  desire  to  calibrate  the  flask  at  20°  C.  At 
20°  C.,  1000  true  cubic  centimeters  of  water  weigh  998.26  grams  in 
vacuum,  and  the  correction  for  air  displacement,  as  seen  above,  is 
1.06  grams.  Then  998.26—  1.06  =  997.2  grams,  and  represents  the 
weight  that  must  be  put  upon  the  pan  of  the  balance  to  be  equal 
to  the  weight  of  the  water  that  occupies  the  volume  of  1000  true 
cubic  centimeters,  or  one  liter,  at  20°  C. 

When  the  calibration  is  expressed  in  true  cubic  centimeters,  the 
weight  of  the  water  in  vacuum  must  be  calculated  because  the  unit 
of  volume  is  weighed  under  these  conditions.  The  following  table, 
which  is  given  to  facilitate  the  calculations  involved,  contains  the 
weight  in  air  of  one  true  cubic  centimeter  of  water,  and  the  volume 
in  true  cubic  centimeters  corresponding  to  the  weight  in  air  of  one 
cubic  centimeter  of  water  at  temperatures  from  10°  to  30°. 


VOLUMETRIC  ANALYSIS 


45 


TEMPERATURE 

WEIGHT  IN  AIR  OF  i  c.c.  OF 

WATER 

VOLUME    CORRESPONDING    TO 
THE  WEIGHT  IN  AIR  OF 
i  GRAM  OF  WATER 

10° 

0.9986  gram 

1.0014  c.c. 

11° 

0.9985 

I.OOI5 

12° 

0.9984 

1.  00l6 

13° 

0.9983 

I.OOI7 

14° 

0.9982 

I.OOlS 

15° 

0.9981 

I.OOI9 

16° 

0.9979 

1.  002  1 

17° 

09977 

1.0023 

1  8° 

0.9976 

1.0024 

19° 

0.9974 

1  .0026 

20° 

0.9972 

.0028 

21° 

0.9970 

.0030 

22° 

0.9967 

•0033     . 

23° 

09965 

.0035 

24° 

0.9963 

.0037 

25° 

0.9960 

.0040 

26° 

0.9958 

.0042 

27° 

0.9955 

.0045 

28° 

0.9952 

.0048 

29° 

0.9949 

.0051 

30° 

0.9946 

.0054 

EXERCISE  IX  _ 

The  Calibration  of  a  Burette 

Clean  the  burette  thoroughly  with  the  chromic  acid  cleaning 
mixture  l  and  then  with  water,  so  that  the  water  will  not  stand  in 
drops  on  the  inner  surface,  but  runs  down  freely.  Boil  about  500 
c.c.  of  distilled  water,  cool,  and  allow  to  stand  until  it  has  acquired 
the  temperature  of  the  laboratory.  Take  the  temperature  with  an 
accurate  thermometer,  read  to  the  closest  degree,  and  record  the 
same.  Fill  the  glass-stoppered  burette  with  this  water  and  starting 
at  the  zero  mark,  run  out  a  portion  of  about  5  c.c.  into  a  previously 
weighed  50  c.c.  glass-stoppered  flask.  Read  the  quantity  of  water 
taken  to  y^o"  °f  a  cubic  centimeter  and  weigh  it  to  one  centi- 

1  The  chromic  acid  cleaning  mixture  is  prepared  by  dissolving  25  grams  of  commercial 
sodium  dichromate  in  150  c.c.  of  water  and  adding  100  c.c.  of  concentrated  commercial 
sulphuric  acid.  This  solution  should  be  placed  into  a  glass-stoppered  bottle  and  saved 
for  future  use,  as  it  can  be  used  many  times. 


46 


QUANTITATIVE  ANALYSIS 


gram.  Introduce  into  the  flask  the  second  portion  of  approxi- 
mately 5  c.c.,  representing  the  amount  of  water  between  the  five 
and  ten  cubic  centimeter  marks.  Repeat  this  process  by  remov- 
ing and  weighing  the  successive  five  cubic  centimeter  portions 
until  the  burette  is  emptied.  Now,  refill  and  repeat  the  calibration 
until  the  values  are  accurately  known. 

From  the  values  given  in  the  table  on  page  45,  calculate  the 
volume  in  true  cubic  centimeters  of  these  portions  of  liquid.  Know- 
ing the  volume  as  represented  by  the  burette  reading  and  the 
volume  in  true  cubic  centimeters  as  obtained  from  the  weight, 
the  correction  is  readily  obtained  by  subtraction.  Plot  the  cor- 
rection curves,  using  the  abscissas  for  the  burette  readings  and 
the  ordinates  for  the  corrections. 

Obtain  the  weight  of  the  successive  5  c.c.  portions  taken  from 
the  pinchcock  burette,  calculate  the  volume  in  true  cubic  centi- 
meters, and  plot  the  calibration  curve  as  in  the  case  of  the  glass- 
stoppered  burette. 

The  following  table  represents  a  method  of  recording  the  data 
for  the  calibration  of  a  30  c.c,  burette.  The  headings  of  the 
columns  are  self-explanatory. 

CALIBRATION  OF  THE  PINCHCOCK  BURETTE 
Temperature  of  water  21° 


READINGS 
c.c. 

WEIGHT  OF 
WATER 

VOLUME  IN 
TRUE  CUBIC 
CENTIMETERS 

CORRECTIONS 
ADDITIVE 

0.00 

21.375  weight  of  flask 

5-00 

26.410  weight  of  flask  +  water 

5-035 

5.05 

+  0.05 

10.00 

31.395  weight  of  flask  +  water 

4.985 

5.00 

0.05 

15.00 

36.410  weight  of  flask  +  water 

5.015 

5-03 

0.08 

20.00 

41.415  weight  of  flask  4-  water 

5.005 

5.02 

0.10 

25.00 

46.430  weight  of  flask  +  water 

5-0^5 

5-03 

0.13 

30.00 

51.435  weight  of  flask  +  water 

5.005 

5.02 

0.15 

The  volume  in  true  cubic  centimeters  occupied  by  the  different 
weights  of  water  may  be  readily  calculated  in  the  following  man- 
ner. The  weight  of  the  first  portion  of  water  between  the  zero  and 
the  5  c.c.  mark  was  5.035  grams.  By  consulting  the  table,  page 
45,  it  will  be  found  that  the  weight  in  air  of  one  true  cubic  centi- 
meter of  water  at  21°  is  0.997  gram;  5.035  grams -i- 0.997  =  5-05, 
the  number  of  true  cubic  centimeters  in  the  first  portion.  The 


VOLUMETRIC  ANALYSIS  47 

weight  of  the  second  portion  is  4.985  grams,  and  in  a  similar  man- 
ner we  find  this  equal  to  5.00  c.c.  Continuing  this,  we  obtain  the 
values  for  the  various  portions  as  given  in  next  to  the  last 
column. 

The  values  given  in  the  last  column,  representing  the  additive 
corrections  for  the  successive  5  c.c.  portions,  are  to  be  represented 
graphically  by  means  of  a  curve  known  as  the  Calibration  Curve. 
The  calibration  curve  is  to  be  drawn  so  that  the  corrections  can 
be  read  to  hundredths  of  a  cubic  centimeter  and  so  that  they  are 
additive.  That  is,  for  any  reading  of  the  burette,  the  correction  at 
that  point  is  given  for  the  total  amount  of  liquid  that  has  been  re- 
moved. The  curves  given  in  Fig.  14  illustrate  this  method  of 
drawing  calibration  curves.  The  abscissas  represent  the  burette 
readings  which  can  be  read  direct  to  0.25,  and  the  ordinates  the 
corrections  estimated  to  o.oi  of  a  cubic  centimeter.  The  data  pre- 
sented in  the  above  table  and  given  in  the  last  column  are  plotted 
as  Curve  i,  which  represents  a  convenient  size  and  one  which 
can  be  pasted  upon  the  inside  of  the  cover  of  the  notebook. 

Notes.  —  i.  Be  sure  that  all  air  bubbles  are  removed  from  the 
tips  of  the  burettes. 

2.  From  an  inspection  of  the  values  given  in  the  table,  page  45, 
it  will  be  observed  that  the  temperature  does  not  need  to  be  read 
very  closely.    For  example,  the  difference   between   20°  and  21° 
makes  a  difference  in  the  volume  corresponding  to  a  weight   in 
air  of  one  gram  of  water,  of  0.0002  c.c.,  and  for  5  c.c.  this  would 
amount  to  o.ooi  c.c.,  which  is  much  beyond  the  accuracy  with  which 
the  burette  can  be  read. 

3.  In  using  a  burette  always  run  out  the  liquid  slowly  and  allow 
a  sufficient  length  of  time  to  elapse  to  permit  the  liquid  to  run 
down  from  the  sides  before  taking  the  reading.     About  one  minute 
is  sufficient  when  small  quantities  are  delivered,  and  two  minutes 
when  about  the  total  capacity  of  the  burette  is  delivered. 

4.  Make  the  calibration  curves  of  such  size  that  they  can  be 
pasted  upon  the  inside  of  the  front  cover  of  the  notebook.     This 
is  done  by  using  as  the  scale  for  the  correction  ten  divisions  of 
approximately  one  millimeter  for  o.i  c.c.,  and  the  same  for  each 
2.5  c.c.  of  the  burette  reading. 

5.  Burettes  may  be  conveniently  calibrated  against  a  burette  or 
vessel,  the  capacity  of  which  has  been  accurately  determined  by 


VOLUMETRIC  ANALYSIS  49 

weighing.  For  this  purpose,  the  Ostwald  Calibrating  Apparatus  is 
frequently  employed.1  For  the  calibration  of  burettes  and  flasks 
the  Morse-Blalock 2  Bulbs  are  often  used,  and  are  excellent  when 
much  of  this  work  is  to  be  done. 

STANDARD    AND  NORMAL   SOLUTIONS 

A  Standard  Solution  is  one  in  which  the  contents  of  a  definite 
volume  are  accurately  known.  The  strength  of  a  standard  solution 
is  expressed  in  various  ways.  If  58.5  grams,  the  molecular  weight, 
of  sodium  chloride  are  dissolved  and  made  up  to  a  liter,  one  cubic 
centimeter  will  contain  0.0585  gram,  which  is  ^he  strength  of  the 
solution.  Such  a  solution  would  contain  35.45  grams  of  chlorine 
per  liter,  i.e.,  0.03545  gram  per  cubic  centimeter.  The  strength 
may  be  stated  either  in  terms  of  sodium  chloride  or  of  chlorine. 
The  customary  way  of  expressing  the  strength  of  a  solution  is  to 
state  it  in  terms  of  one  of  the  constituents ;  but  it  may  also  be 
stated  in  terms  of  the  quantity  of  a  substance  to  which  it  is  chemi- 
cally equivalent  and  which  is  to  be  estimated  by  the  use  of  the 
standard.  Sodium  chloride  reacts  with  silver  nitrate  according  to 
the  following  equation  : 

NaCl  +  AgNO3  =  AgCl  +  NaNO3, 

i.e.,  one  combining  weight  of  chlorine  is  equivalent  to  one  combin- 
ing weight  of  silver,  or  35.45  grams  of  chlorine  are  equal  to  107.93 
grams  of  silver  ;  and  0.10793  grain  of  silver,  which  is  contained  in 
one  cubic  centimeter  of  the  solution,  is  equivalent  to  0.03545  gram 
of  chlorine.  We  could  state  then  that  one  cubic  centimeter  of  the 
sodium  chloride  solution  is  equivalent  to  0.10793  gram  of  silver. 
To  a  special  kind  of  standard  solution  the  term  normal  solution 
is  applied.  If  the  molecular  weight  of  hydrochloric  acid  (36.458 
grams)  be  dissolved  in  water  and  the  solution  made  up  to  1000  true 
cubic  centimeters,  we  would  have  a  liter  of  a  hydrochloric  acid  solu- 
tion which  would  contain  1.008  grams  of  replaceable  hydrogen,  or 
one  combining  weight  of  hydrogen.  One  half  the  molecular  weight 
in  grams  of  sulphuric  acid  would  also  furnish  one  combining  weight 
of  hydrogen,  or  1.008  grams.  If  this  quantity  of  sulphuric  acid 
were  dissolved  and  made  up  to  one  liter,  we  would  have  an  acid 

1  Tread  well- Hall,  Analytical  Chemistry,  II,  417  (1906). 

2  Morse,  Exercises  in  Quantitative  Chemistry,  p.  85  (1905). 
E 


50  QUANTITATIVE  ANALYSIS 

solution  of  the  same  strength  as  the  hydrochloric  acid  solution. 
These  solutions  would  contain  the  same  number  of  grams  of  the 
replaceable  hydrogen  per  liter.  Solutions  which  contain  one  com- 
bining weight  of  replaceable  hydrogen  per  true  liter  are  termed 
Normal  Acid  Solutions.  The  molecular  weight  of  sodium  hydrox- 
ide would  neutralize  the  molecular  weight  of  hydrochloric  acid ;  it 
follows,  therefore,  that  if  the  gram  molecular  weight  of  sodium 
hydroxide  were  dissolved  and  made  up  to  a  liter,  that  these  1000  c.c. 
would  neutralize  loooc.c.  of  the  normal  hydrochloric  acid  solution, 
i.e.,  the  two  solutions  would  be  equal  chemically,  cubic  centimeter  for 
cubic  centimeter.  The  same  may  be  stated  concerning  a  solution 
looo  c.c.  of  which  contain  the  gram  molecular  weight  of  potassium 
hydroxide  and  the  normal  solution  of  sulphuric  acid.  It  is  custom- 
ary to  designate  alkali  solutions  which  contain  the  equivalent  of 
one  combining  weight  of  replaceable  hydrogen  per  true  liter, 
Normal  Alkali  Solutions. 

In  solutions  used  for  oxidation  processes  the  oxygen  furnished 
is  the  important  factor,  and  since  one  combining  weight  of  oxygen 
oxidizes  two  combining  weights  of  hydrogen,  these  solutions  can 
be  conveniently  expressed  as  normal  solutions.  A  liter  of  a  solu- 
tion of  potassium  permanganate  which  furnishes  for  oxidation 
purposes  8  grams  of  oxygen,  i.e.,  0.008  gram  per  cubic  centime- 
ter, is  equivalent  to  one  combining  weight  of  hydrogen,  and, 
therefore,  is  a  normal  potassium  permanganate  solution.  When 
the  molecular  weight  of  the  substance  is  dissolved  and  made  up 
to  a  true  liter,  the  solution  is  a  gram  molecular  solution.  In  many 
cases  this  is  the  same  as  a  normal  solution,  as  in  the  case  of  hydro- 
chloric acid,  sodium  hydroxide,  acetic  acid,  and  potassium  chloride ; 
but  in  many  other  cases  they  are  not  the  same,  —  for  example, 
sulphuric  acid  and  potassium  dichromate.  As  a  result,  consider- 
able confusion  has  arisen  in  the  literature  and  unfortunately  the 
terms  normal  and  molecular  are  not  distinguished ;  but  normal  is 
sometimes  used  when  gram  molecular  is  meant. 

Normal  solutions  are  usually  too  concentrated  to  be  conveniently 
employed  and  fractional  parts  of  the  amount  of  the  substance  re- 
quired to  make  a  normal  solution  are  used  instead.  If  one-half  of 
the  molecular  weight  of  hydrochloric  acid  is  contained  in  a  liter, 
this  is  a  half-normal  solution  and  is  expressed  as  N/2  HC1.  If 
one-tenth  the  molecular  weight  is  taken,  the  solution  is  tenth- 
normal,  N/io,  and  so  on. 


VOL  UME  TRIG  ANAL  YSIS  5 1 

An  error  sometimes  results  from  using  these  solutions  at  tem- 
peratures different  from  that  at  which  they  were  prepared.  The  so- 
lutions are  usually  made  up  at  a  certain  temperature  (about  20°  C), 
and  then  stored  in  bottles  from  which  they  are  removed  when  de- 
sired. One  such  solution  of  hydrochloric  acid  was  found  to  have 
a  temperature  of  33°,  or  an  increase  of  13°  over  the  temperature 
at  which  it  was  prepared.  If  we  assume  that  the  change  between 
20-30°  is  the  same  as  that  between  15-25°,  one  liter  of  this  acid 
would  then  occupy  1002.42  c.c.  If  the  molecular  weight  (36.46 
grams)  of  hydrochloric  acid  were  contained  in  one  liter  at  20°,  at 
30°  it  would  be  dissolved  in  1002.42  c.c.,  or  in  the  first  case,  one 
cubic  centimeter  would  contain  0.03646  gram,  and  in  the  second 

— =0.03637.     Now,  in  titrating,  if  at  20°,  25  c.c.  of  the  solution 
1002.42 

would  be  required,  at  30°  it  would  take  25.06  c.c.  to  furnish  the 
same  quantity  of  acid.  This  difference  is  greater  than  the  allowable 
experimental  error,  as  the  burette  can  be  read  direct  to  o.oi  c.c. 

The  following  table1  gives  the  expansion  of  1000  c.c.  of  various 
solutions  due  to  a  change  of  temperature  from  15°  to  25°: 


• 

SOLUTION 

EXPANSION 

Water 

2.OC 

N 

HC1                

2.4.2 

N 

H2SO4                

•3.QC 

N 

2.62 

N 

NaOH                                                     

•J.I  r 

N 

Na.COo 

O'1  J 

N 

NaCl    

2.12 

N/io 

NaCl    

2.06 

N/io 

2.l6 

N/io 

KMnO4         

2.13 

ACIDIMETRY   AND    ALKALIMETRY 

The  processes  of  acidimetry  and  alkalimetry  comprise  the  deter- 
minations of  acids  and  alkalies  (hydroxides  and  carbonates). 
When  an  acid  is  to  be  determined,  a  standard  alkali  solution  is 
employed;  and  when  the  sample  is  analyzed  for  hydroxides  or 
carbonates,  a  standard  acid  is  used.  The  process  of  bringing  the 

iSchultz,  Zeit.  fur  Anal.  Chem.,  21,  167. 


52  QUANTITATIVE  ANALYSIS 

solutions  of  the  reacting  substances  together  is  termed  Titration. 
The  neutral  point,  or,  in  general,  the  point  which  represents  the 
completion  of  the  reaction,  is  desigated  as  the  End  Point. 

INDICATORS 

The  end  of  the  reaction  is  made  apparent  to  the  eye  by  means 
of  indicators  whose  colors  in  acid  and  in  alkaline  solutions  are 
different.  These  indicators  are  usually  solutions  of  organic  com- 
pounds which  are  added  directly  to  the  solution  to  be  titrated. 
There  is  no  substance  which  can  be  used  as  a  universal  indicator, 
consequently,  different  indicators  must  be  used  for  the  titration  of 
the  various  acids  and  alkalies.  The  following  are  the  most  impor- 
tant indicators  used  in  the  determinations  of  this  kind. 

Litmtis.  This  is  a  vegetable  coloring  matter,  usually  employed 
in  the  form  of  the  aqueous  extract.  It  gives  a  red  color  with  acids, 
while  with  alkalies  a  blue  color  is  produced.  Besides  its  applica- 
tion to  the  titration  of  the  ordinary  acids  and  alkalies,  it  may  also 
be  used  for  weak  acids  and  in  the  presence  of  ammonium  salts. 
Solutions  containing  carbon  dioxide  must  be  boiled,  as  litmus  is 
not  reliable  when  used  in  its  presence.  ,  , 

Phenolphthalein  is  an  organic  compound  which  is  produced 
synthetically.  It  is  used  in  the  form  of  an  alcoholic  solution.  In 
acid  solutions  this  indicator  forms  a  colorless  compound,  while  in 
alkaline  solutions  the  products  are  red.  It  finds  special  applica- 
tion with  the  weak  acids,  such  as  hydrogen  sulphide  and  the 
organic  acids.  Carbon  dioxide  must  be  expelled  from  the  solution 
by  boiling,  before  the  indicator  can  be  used.  It  is  not  reliable 
when  used  for  the  titration  of  weak  alkalies  like  ammonium  hy- 
droxide. 

Methyl  Orange  is  an  organic  substance  which  in  aqueous  solu- 
tion produces  a  red  coloration  with  acids  and  a  yellow  coloration 
with  alkalies.  In 'neutral  solution  there  is  a  rich  golden  brown 
tint  which  can  be  easily  recognized.  This  indicator  is  very  satis- 
factory for  the  titration  of  the  inorganic  acids.  It  is  not  affected 
by  carbon  dioxide  nor  hydrogen  sulphide  in  cold  solution,  and  con- 
sequently may  be  used  in  their  presence.  For  the  weaker  organic 
acids,  such  as  tartaric  and  oxalic,  it  is  not  reliable.  It  may  also  be 
used  for  the  titration  of  solutions  of  ammonium  hydroxide. 

Cochineal.     This  indicator  is  used  in  the  form  of  an  alcoholic 


VOLUMETRIC  ANALYSIS 


53 


extract  made  from  the  cochineal  insect.  With  acids  the  color  of 
the  solution  is  red.  This  turns  to  a  violet  color  when  the  solution 
is  made  alkaline.  It  cannot  be  used  in  the  presence  of  iron  or 
aluminium  or  acetates.  It  is  especially  valuable  for  the  titration 
of  ammonium  hydroxide. 

Note.  —  Since  the  different  indicators  require  different  amounts 
of  alkali  or  acid  to  produce  the  change  in  color,  the  same  indicator 
should  be  used  in  the  analysis  as  in  the  standardization  ;  moreover, 
an  excess  of  the  indicator  should  not  be  used.  A  few  drops  are 
usually  sufficient. 

NOTEBOOKS 

The  volumetric  experimental  data  should  be  recorded  in  a  system- 
atic manner.  A  satisfactory  method  of  arrangement  is  represented 
in  Fig.  15.  On  the  right-hand  page  the  readings  of  the  burettes 


3'3" 

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FIG.  15 

and  the  ratios  of  the  solutions  are  recorded.  Before  recording 
the  burette  readings  make  the  necessary  corrections  from  the 
calibration  curves  and  record  the  corrected  readings.  On  the  left- 
hand  page  should  appear  equations  representing  all  of  the  chemical 


54  QUANTITATIVE  ANALYSIS 

changes  and  a  clear,  concise  statement  of  the  calculations,  includ- 
ing all  equations  upon  which  these  are  based. 


PREPARATION  OF  STANDARD  AND  NORMAL  SOLUTIONS 

The  ideal  method  for  the  preparation  of  standard  or  normal  so- 
lutions of  alkalies  and  acids  would  be  to  weigh  out  accurately  the 
calculated  amounts  of  the  substances  required  to  make  the  desired 
quantities  of  these  solutions,  dissolve  in  water,  and  make  up  to  the 
proper  volumes  at  the  specified  temperature.  Unfortunately, 
there  are  very  few  substances  of  a  sufficiently  high  degree  of 
purity  to  be  utilized  in  this  manner.  The  usual  method  of  prepar- 
ing a  standard  solution  is,  therefore,  to  dissolve  the  approximate 
amount  of  the  substance  in  water  and  make  it  up  to  the  required 
volume.  The  exact  strength  of  the  solution  can  then  be  ascer- 
tained in  a  variety  of  ways,  depending  on  whether  it  is  a  solution 
of  an  acid  or  an  alkali. 

The  following  are  some  of  the  more  common  methods  used  for 
the  standardization  of  solutions  : 

(a)  By  precipitation.     If  the  solution  to  be  standardized  contains 
a  constituent  which  can  be  converted  into  an  insoluble  compound, 
the  amount  of  this  constituent,  and  consequently  the  amount  of  the 
compound  in  which  it  occurs,  can  readily  be  determined.     For  ex- 
ample, a  hydrochloric  acid  solution  can  be  standardized  by  pre- 
cipitating the  chlorine  in  a  definite  volume  as  silver  chloride,  and 
from  the  weight  of  the  precipitate,  the  hydrochloric  acid  in  one 
cubic  centimeter  of  the  solution  can  be  calculated.     Again,  a  solu- 
tion of  sulphuric  acid  can  be  standardized  by  precipitating  with 
barium  chloride,  and  from  the  weight  of  barium  sulphate  obtained, 
the  amount  of  sulphuric  acid  in  one  cubic  centimeter  can  be  calcu- 
lated.    A  barium  hydroxide  solution  can  be  standardized  by  pre- 
cipitating   as    barium    sulphate,    and    from    the    weight   of   the 
precipitate  the  barium  hydroxide  in  one  cubic  centimeter  of  the 
solution   can    be   readily   ascertained.     The    application   of    this 
method  is  limited. 

(b)  By  titration.     I.    Against  a  solution  that  has  been  standard- 
ized very  accurately  by  precipitation,  such  as  barium  hydroxide, 
hydrochloric  acid,  or  sulphuric  acid. 

2.  Against  the  purest  chemicals  obtainable.  For  standardizing 
the  alkalies,  the  substances  usually  employed  are  pure  oxalic  acid, 


VOLUMETRIC  ANALYSIS  55 

tartaric  acid,  acid  oxalates,  and  potassium  acid  tartrate ;  for  acids, 
Iceland  spar,  pure  precipitated  calcium  carbonate,  and  pure  dry 
sodium  carbonate  obtained  by  heating  the  bicarbonate. 

(c)  By  the  absorption  method.  A  known  weight  of  a  volatile 
gas,  such  as  hydrochloric  acid  or  ammonia,  is  absorbed  in  water  and 
the  solution  made  up  to  a  definite  volume. 


EXERCISE  X 

Preparation  of  an  Approximately  Half-Normal  Hydrochloric  Acid 

Solution 

Procedure.  —  Obtain  a  sample  of  hydrochloric  acid,  a  250  c.c. 
graduated  cylinder,  a  hydrometer,  and  a  thermometer.  Introduce 
into  the  graduated  cylinder  sufficient  hydrochloric  acid  solution  to 
float  the  hydrometer.  Place  the  cylinder  under  the  water  tap  and 
allow  the  water  to  run  upon  it,  making  sure  that  no  water  runs 
into  the  cylinder.  If  the  tap  water  is  not  cold  enough,  use  a 
beaker  of  ice  water  for  cooling.  Stir  the  acid  occasionally  by 
means  of  the  thermometer,  and  cool  to  15°  C,  then  read  the  hydrom- 
eter very  carefully  by  noting  the  place  on  the  hydrometer  stem 
which  is  on  a  line  with  the  surface  of  the  liquid.  Be  sure  that  the 
hydrometer  is  free  to  move  and  does  not  touch  the  sides  of  the 
cylinder.  Record  the  reading,  which  gives  the  specific  gravity  of 
the  liquid.  Now  consult  the  table  of  specific  gravities  of  hydro- 
chloric acid  on  page  203,  and  ascertain  the  percentage  of  hydro- 
chloric acid  corresponding  to  this  specific  gravity.  From  these 
data  calculate  the  number  of  cubic  centimeters  of  this  solution  that 
will  be  required  to  make  two  liters  of  a  half -normal  hydrochloric 
acid  solution.  Measure  out  this  quantity  by  means  of  the  gradu- 
ated cylinder,  pour  into  a  liter  flask,  fill  to  the  upper  mark,  and 
then  transfer  to  a  2j  liter  glass-stoppered  bottle.  Add  another 
liter  of  water,  and  shake  the  contents  of  the  bottle  very  thoroughly 
to  insure  a  homogeneous  solution.  Label  the  bottle  Hydrochloric 
Acid  Solution. 

Note.  —  The  density  of  the  solution  changes  with  the  tempera- 
ture, hence  the  necessity  of  controlling  the  temperature  during  the 
determination  of  the  specific  gravity. 


56  QUANTITATIVE  ANALYSIS 

EXERCISE   XI 

Preparation  of  an  Approximately  Half -Normal  Potassium  Hydroxide 

Solution 

Procedure.  —  On  the  assumption  that  the  sample  of  potassium 
hydroxide  to  be  used  is  85  per  cent  pure,  calculate  the  number  of 
grams  required  to  make  two  liters  of  a  half-normal  solution  of 
potassium  hydroxide.  Weigh  out  quickly  into  a  No.  4  beaker  on 
the  rough  balance  five  grams  more  than  the  calculated  amount, 
transfer  quickly  to  a  2\  liter  glass-stoppered  bottle,  containing  two 
liters  of  water,  shake  vigorously  to  insure  a  homogeneous  liquid. 
Replace  the  glass  stopper  by  a  cork  and  label  Potassitim  Hydrox- 
ide Solution. 

Note.  —  Solutions  of  the  caustic  alkalies  should  not  be  kept  in 
vessels  having  ground  glass  stoppers,  owing  to  the  fact  that  the 
alkali  attacks  the  glass  and  often  cements  the  stopper  so  that  it 
cannot  be  removed. 

EXERCISE   XII 

The  Titration  of  the  Acid  against  the  Alkali 

Establish  the  ratio  between  the  two  solutions  in  the  following 
manner :  Having  thoroughly  cleaned  the  burettes  so  that  when 
the  water  is  run  out  there  wtill  be  no  drops  remaining  on  the  inner 
walls,  rinse  the  glass-stoppered  burette  three  times  with  5  c.c. 
portions  of  the  hydrochloric  acid  solution  and  fill  it  above  the  zero 
mark.  In  a  similar  manner  rinse  and  fill  the  pinchcock  burette 
with  the  potassium  hydroxide  solution.  Now  run  out  the  liquids 
from  the  burettes  until  the  lower  surface  of  the  meniscus  stands 
exactly  at  the  zero  mark,  making  sure  that  the  tips  contain  no  air 
bubbles.  Into  a  clean  Erlenmeyer  flask  containing  about  20  c.c. 
of  water  introduce  about  20  c.c.  of  the  acid,  add  a  few  drops 
(three  or  four)  of  the  methyl  orange  indicator,  and  then  run  in  the 
potassium  hydroxide  slowly  until  the  solution  becomes  yellow, 
shaking  it  meanwhile.  This  indicates  that  the  solution  is  alkaline, 
and  that  an  excess  of  the  potassium  hydroxide  has  been  introduced. 
Wash  down  the  sides  of  the  flask  with  distilled  water  and  add  acid 
drop  by  drop  until  one  drop  changes  the  solution  from  yellow  to 
a  golden  brown  tint  which  is  the  end  point.  Then  record  the 


VOL  UMETRIC  ANAL  YSIS  5  7 

readings  of  the  burettes.  Since  the  reading  includes  all  the  liquid 
run  out  of  the  burette,  the  drop  remaining  on  the  tip  should  be  re- 
moved by  means  of  a  stirring  rod  and  added  to  the  flask  before  the 
end  point  is  established.  Again  fill  the  burettes  to  the  zero  mark 
with  their  respective  solutions  and  repeat  the  titration,  using  a 
clean  Erlenmeyer  flask.  Make  three  such  titrations  and  record 
the  individual  results.  It  is  a  good  plan  to  record  them  in  the 
same  order  in  which  the  burettes  are  placed.  If  the  acid  burette 
is  on  the  right,  record  the  readings  of  this  burette  on  the  right  side 
of  the  page.  (See  Fig.  15.)  Now  calculate  the  ratio  of  each  of 
these  titrations,  expressing  it  in  terms  of  the  number  of  cubic  cen- 
timeters of  the  potassium  hydroxide  solution  equal  to  one  cubic 
centimeter  of  the  acid.  These  values  should  not  vary  more  than 
two-tenths  of  a  per  cent  of  the  total  ratio.  Take  the  average  of  the 
ratios  as  the  true  relation  between  the  two  solutions. 

STANDARDIZATION   OF   THESE   SOLUTIONS 

The  relation  between  these  two  solutions  has  been  established, 
but  it  is  also  necessary  to  know  their  exact  strengths,  that  is,  the 
number  of  grams  of  the  respective  constituents  present  in  one 
cubic  centimeter. 

EXERCISE  XIII 

Standardization  of  the  Hydrochloric  Acid  Solution 

a.    By  Precipitation  of  the  Chlorine  as  Silver  Chloride 

Procedure.  —  Measure  from  the  burette  into  two  No.  2  beakers 
from  10  to  15  c.c.  of  the  hydrochloric  acid  solution,  record 
the  exact  amounts  taken,  and  precipitate  the  chlorine  in  the 
manner  described  in  Exercise  V,  page  24.  Filter  by  means  of  a 
Gooch  crucible. 

Preparation  of  the  Gooch  Crucible.  —  Obtain  from  the  supply 
room  two  Gooch  crucibles  with  perforated  plates,  two  Gooch  fun- 
nels and  rubbers,  and  the  outfit  for  filtering  by  suction,  consisting 
of  two  filter  flasks  with  stoppers,  a  T-tube,  a  suction  pump,  and 
three  pieces  of  rubber  tubing.  Place  the  funnel  in  the  neck  of 
the  filter  flask  by  means  of  the  rubber  stopper,  stretch  the  rubber 
band  over  the  funnel,  and  place  the  crucible  into  the  opening. 
Arrange  as  shown  in  Fig.  16,  and  connect  with  the  filter  pump. 


58      -.  QUANTITATIVE  ANALYSIS 

Pour  an  emulsion  of  asbestos  (which  has  been  digested  with  hydro- 
chloric acid  and  washed  free  from  the  same)  into  the  crucibles  so 
that  a  layer  I  to  2  mm.  thick  will  be  formed.  Place  the  perforated 
plates  upon  this,  and  wash  with  hot  water  to  remove  any  loose 
fibers  of  asbestos.  Wash  finally  with  alcohol.  Too  great  a  suction 


FIG.  16 


should  not  be  used,  since  it  packs  the  asbestos  mat  so  closely  that 
the  filtration  takes  place  slowly.  Place  the  Gooch  crucibles  into 
small  beakers,  cover  with  cover-glasses,  dry  at  110°  for  forty 
minutes,  cool  in  the  desiccator,  and  weigh.  Replace  in  the  oven 
and  heat  to  constant  weight.  Place  them  in  the  funnels  again  and 
filter  the  silver  chloride  precipitates,  holding  the  stirring  rod  near 
the  bottom  of  the  crucible  while  pouring  the  liquid  into  it. 
Remove  all  the  precipitate  from  the  beaker,  wash  in  the  usual 
manner,  and  finally  wash  with  a  few  cubic  centimeters  of  alcohol. 
Place  the  crucibles  into  the  oven  and  heat  to  constant  weight. 
From  the  weight  of  silver  chloride  calculate  the  amount  of  hydro- 
chloric acid  in  each  cubic  centimeter  of  the  solution  and  also  the 
normality  factor. 

Normality  factor  =  Weight  of  HC1  in  I  c.c.  of  given  solution 
Weight  of  HClin  I  c.c.  of  normal  solution 


VOL UMETRIC  ANAL  YSIS  59 

That  is,  the  normality  factor  is  the  ratio  between  the  number  of 
grams  of  hydrochloric  acid  found  and  the  number  of  grams  there 
should  be  found  if  the  solution  were  normal.  Hence,  to  convert 
the  number  of  cubic  centimeters  of  the  given  solution  used  into 
cubic  centimeters  of  normal  solution,  multiply  by  the  normality 
factor. 

b.    Standardization  of  the  Acid  against  Calcium  Carbonate 

Procedure.  —  Weigh  out  three  very  finely  pulverized  samples  of 
Iceland  spar  of  about  0.5  gram  each  into  properly  labeled  Erlen- 
meyer  flasks.  Introduce  into  each  flask  25-30  c.c.  of  the  hydro- 
chloric acid  solution,  recording  the  exact  amount  used.  Allow  to 
stand  for  several*  hours,  and  when  the  sample  is  completely  dis- 
solved, add  methyl  orange  indicator,  and  titrate  the  excess  of  acid 
with  the  alkali  solution.  Knowing  the  ratio  between  the  acid  and 
alkali,  calculate  the  number  of  cubic  centimeters  of  acid  required 
to  dissolve  each  of  the  samples  of  Iceland  spar.  Assuming  the 
Iceland  spar  to  be  absolutely  pure,  calculate  the  normality  factor 
of  the  acid  solution. 

EXERCISE  XIV 

/ 

Standardization  of  the  Alkali  Solution 

a.   Against  some  of  the  Pure  Chemicals  Available  for  this  Purpose 

Procedure.  —  Weigh  out  accurately  7-8  grams  of  pure  oxalic 
acid  (H2C2O4  •  2H2O),  or  8-10  grams  of  tartaric  acid  (H2C4H4O6). 
Dissolve  in  water,  transfer  to  a  250  c.c.  flask,  make  up  to  the  mark, 
and  shake  thoroughly  to  insure  a  homogeneous  liquid.  Fill  the 
glass-stoppered  burette  with  this  solution,  and  run  out  about  25  c.c. 
into  a  250  c.c.  casserole  containing  about  25  c.c.  of  water.  Heat 
to  boiling,  add  a  few  drops  of  phenolphthalein,  and  titrate  with  the 
alkali  solution  until  the  pink  color  appears.  Add  one  cubic  centi- 
meter of  the  acid  solution  and  boil  for  one  minute.  Then  to  the 
hot  solution  add  potassium  hydroxide  solution  until  one  drop 
causes  the  solution  to  change  to  a  faint  pink  color  which  lasts  for 
several  minutes.  Repeat  until  the  relation  between  the  solutions 
has  been  accurately  established.  Write  the  equations  representing 
the  chemical  reaction,  and,  assuming  that  this  sample  of  oxalic 


60  QUANTITATIVE  ANALYSIS 

acid  (or  tartaric  acid)  is  absolutely  pure,  calculate  the  normality 
factor  of  the  alkali  solution. 

Using  phenolphthalein  as  the  indicator,  establish  the  relation 
between  the  standard  hydrochloric  acid  and  the  potassium  hydrox- 
ide solutions  in  the  manner  just  described.  From  this  ratio  and 
the  value  obtained  for  the  alkali  and  the  oxalic  acid  calculate  the 
normality  of  the  hydrochloric  acid  solution.  Compare  this  with  the 
values  obtained  by  the  two  methods  for  standardizing  the  acid. 

Notes. —  i.  The  result  obtained 'when  phenolphthalein  is  used 
may  be  slightly  different  from  that  obtained  with  the  use  of 
methyl  orange.  The  indicator  used  in  the  standardization  should 
be  the  same  as  that  used  in  all  the  determinations. 

2.  The  distilled  water  may  contain  carbon  dioxide,  especially 
if  blown  from  the  wash  bottle  by  air  from  the  lungs.     Moreover, 
the  sample  of  potassium  hydroxide  may  contain  a  certain  amount 
of  carbonate  which  liberates  carbon  dioxide  when  oxalic  acid  is 
added.     It  is,  therefore,  necessary  to  expel  the  carbon  dioxide  by 
heating  the  solution,  as  it  gives  an  acid  reaction  toward  phenol- 
phthalein. 

3.  If  the  solution  is  heated  in  a  glass  vessel,  enough  alkali  may 
be  dissolved  from  the  glass  to  make  an  appreciable  error  in  the 
determination.     It  is  necessary,  therefore,  to  use  porcelain  casse- 
roles, which  do  not  dissolve  under  these  conditions. 

b.  By  the  Absorption  Method 

Principle.  —  This  method  depends  on  absorbing  pure  hydrochlo- 
ric acid  gas  in  a  weighed  quantity  of  water,  which  is  then  weighed 
and  made  up  to  a  definite  volume.  This  gives  a  standard  solution 
which  may  be  employed  in  the  standardization  of  alkali  solutions. 

Procedure.  —  Obtain  two  absorption  flasks  and  their  correspond- 
ing drying  tubes,  which  are  filled  with  granular  calcium  chloride. 
These  are  represented  by  Fig.  17  and  are  readily  prepared  from 
100  c.c.  Erlenmeyer  flasks  and  common  calcium  chloride  tubes. 
The  tube  through  which  the  gas  enters  may  be  drawn  out  or  blown 
into  a  bulb  in  which  a  number  of  perforations  are  made.  After  the 
flasks  have  been  thoroughly  cleaned,  introduce  about  25  c.c.  of 
water  into  each.  This  should  be  sufficient  to  immerse  the  end  of 
the  delivery  tube  to  the  depth  of  about  one  centimeter,  when  the 


VOLUMETRIC  ANALYSIS 


6l 


tube  is  nearly  touching  the  bottom  of  the  flask.     Weigh  the  flasks 
in  the  following  manner  : 

Place  one  flask  and  drying  tube  upon  the  left  pan  of  the  bal- 
ance, and  the  other  upon  the  right  pan.  Determine  carefully 
whether  the  flask  on  the  left  pan  is  heavier ;  if  not,  reverse  their 


FIG.  17 

positions,  and  add  enough  weights  to  produce  equilibrium.  The 
weights  used  represent  the  excess  in  weight  of  the  heavier  flask, 
which  is  marked  A,  over  that  of  the  lighter,  B.  Take  A  to  the 
hydrochloric  acid  generator  and  after  removing  the  sealing  plugs 
a  and  b,  attach  it  to  the  hydrochloric  acid  generator  by  means  of 
the  long  delivery  tube.  Immerse  the  absorption  flask  in  water  and 
then  start  the  flow  of  gaseous  hydrochloric  acid  by  allowing  con- 
centrated hydrochloric  acid  to  drop  slowly  into  pure  concentrated 
sulphuric  acid.  Keep  a  fairly  rapid  constant  stream  of  gas  bub- 
bling through  the  concentrated  sulphuric  acid  wash  bottles  for  about 


62  QUANTITATIVE  ANALYSIS 

fifteen  minutes.  Do  not  allow  it  to  stop,  or  it  may  suck  back.  Dis- 
connect and  insert  the  plugs  a  and  b,  before  shutting  off  the  gas. 
Having  wiped  the  flask  dry  and  allowed  it  to  acquire  the  same  tem- 
perature as  the  balance,  put  it  back  upon  the  left  pan  with  B 
upon  the  right  and  add  enough  weights  to  produce  equilibrium. 
The  increase  in  the  excess  of  A  over  B  represents  the  hydro- 
chloric acid  gas  absorbed  in  A.  This  should  not  be  less  than 
five  grams.  Leaving  A  as  it  is,  repeat  the  absorption  manipula- 
tion with  B.  Reweigh  as  before,  with  B  still  on  the  right  pan. 
The  decrease  in  excess  of  A  over  B  represents  the  hydrochlo- 
ric acid  gas  absorbed  in  B.  Be  sure  a  record  has  been  made 
of  all  weights.  Now,  carefully  transfer  the  solution  in  A  to  a 
250  c.c.  graduated  flask.  Rinse  the  flasks  and  delivery  tubes  and 
transfer  all  of  the  rinse  water  to  the  graduated  flask.  Finally 
make  up  to  the  mark  with  distilled  water,  shake  thoroughly  to  in- 
sure a  homogeneous  solution,  and  determine  the  ratio  between  this 
solution  and  the  potassium  hydroxide  solution  by  at  least  three 
titrations.  Transfer  the  contents  of  B  to  a  250  c.c.  graduated 
flask  and  proceed  as  in  the  case  of  A.  Assuming,  upon  the 
basis  of  the  grams  of  gas  absorbed,  that  each  of  the  hydrochloric 
acid  solutions  is  an  accurately  known  standard  solution,  calculate 
from  the  ratio  determined  the  normality  factor  of  the  potassium 
hydroxide  solution. 

Note.  —  For  the  generation  of  the  hydrochloric  acid  gas  any  con- 
venient form  of  apparatus  may  be  used.  The  success  of  the  method 
described  depends  to  a  considerable  extent  upon  the  complete  dry- 
ing of  the  gas. 

EXERCISE  XV 
Determination  of  the  Percentage  Strength  of  Acid  Solutions 

Procedure.  —  Obtain  a  250  c.c.  graduated  cylinder,  a  thermometer, 
a  hydrometer,  and  a  solution  of  one  of  the  following  acids :  hydro- 
chloric, sulphuric,  or  nitric.  Determine  the  specific  gravity  as 
described  in  Exercise  X,  page  55  ;  take  25  c.c.,  transfer  to  a  250 
c.c.  graduated  flask,  make  up  to  the  mark,  mix  thoroughly,  and 
titrate  against  a  standard  alkali  solution.  From  the  data  calculate 
the  percentage  of  the  acid  in  the  solution. 


VOL  UMETRIC  ANAL  YSIS  63 

EXERCISE  XVI 
Analysis  of  a  Soluble  Carbonate 

Procedure.  —  Obtain  in  a  weighing  tube  a  sample  of  a  soluble 
carbonate.  Weigh  in  the  usual  manner  5-10  grams  of  the 
sample  into  a  No.  2  beaker,  dissolve  in  about  100  c.c.  of  water, 
and  introduce  into  a  250  c.c.  graduated  flask.  Make  up  to  the 
mark,  mix  thoroughly,  and  titrate  against  a  standard  acid  solution, 
using  the  proper  indicator.  Write  the  equation  representing  the 
chemical  reaction.  From  the  ratio  established  calculate  the 
percentage  purity  of  the  sample  taken. 

EXERCISE  XVII 

The  Determination  of  Total  and  Caustic  Alkali  in  a  Mixture  of 
Sodium  Hydroxide  and  Sodium  Carbonate 

Principle.  —  When  a  solution  containing  sodium  hydroxide  and 
sodium  carbonate  is  titrated  with  an  acid,  using  phenolphthalein  as 
an  indicator,  the  neutralization  takes  place  in  the  following  stages. 
The  sodium  hydroxide  is  first  neutralized,  then  the  sodium  carbonate 
is  changed  to  the  bicarbonate  : 

NaOH  +  HC1  =  NaCl  +  H2O, 
Na2CO3  +  HC1  =  NaHCO3  +  NaCl. 

When  the  above  reactions  are  complete,  the  addition  of  more  acid 
liberates  carbon  dioxide,  which  decolorizes  the  solution.  If  methyl 
orange  is  now  added,  the  other  half  of  the  carbonate  may  be 
titrated. 

NaHCO3  +  HC1  =  NaCl  +  H2O  +  CO2. 

The  amount  of  acid  used  in  titrating  with  the  phenolphthalein 
represents  all  of  the  sodium  hydroxide,  and  one  half  the  sodium 
carbonate ;  that  used  with  the  methyl  orange  represents  the  other 
half  of  the  sodium  carbonate. 

Procedure. — Weigh  into  a  No.  %  beaker  from  5-10  grams  of 
the  sample.  Dissolve  in  about  100  c.c.  of  water,  transfer  to  a  250 
c.c.  graduated  flask,  and  make  up  to  the  mark  at  room  temperature. 
Remove  by  means  of  a  burette  or  pipette  25  c.c.  of  the  solution, 


64  QUANTITATIVE  ANALYSIS 

introduce  into  an  Erlenmeyer  flask,  and  add  a  few  drops  of 
phenolphthalein.  Place  the  flask  in  ice  water  and  titrate  with  half 
normal  hydrochloric  acid,  shaking  gently  to  mix  the  solutions. 
The  acid  should  be  introduced  under  the  surface  of  the  liquid  by  ex- 
tending the  tip  of  the  burette  by  means  of  a  piece  of  glass  tubing  of 
small  bore.  When  the  solution  becomes  colorless,  record  the  amount 
of  acid  used,  then  add  a  few  drops  of  methyl  orange  and  continue  the 
titration  until  the  characteristic  golden  brown  tint  appears.  Record 
the  total  amount  of  acid  used  and  add  one  more  drop  to  prove  that 
the  neutral  point  has  been  reached.  Repeat  this  until  the  ratio 
has  been  accurately  established.  During  this  last  titration  the 
solution  used  need  not  be  kept  cold.  From  the  data,  calculate  the 
percentage  of  sodium  carbonate,  the  percentage  of  sodium  hydrox- 
ide, and  also  the  total  alkalinity  of  the  sample  expressed  as 
percentage  of  sodium  oxide. 

Notes. —  i.  The  quantitative  formation  of  the  bicarbonate  from 
the  carbonate  takes  place  only  at  o°,  hence  the  solution  must  be 
maintained  at  this  temperature  during  the  titration. 

2.  If  the  acid  is  dropped  into  the  solution,  some  of  the  carbon 
dioxide  from  the  bicarbonate  will  be  lost  and  too  much  acid  will  be 
used  before  the  end  point  represented  by  the  phenolphthalein  is 
reached. 

OXIDATION   AND    REDUCTION 

In  addition  to  the  processes  considered  under  acidimetry  and 
alkalimetry,  there  is  a  large  class  of  important  volumetric  methods 
which  are  based  upon  the  oxidation  or  the  reduction  of  the  substance 
to  be  determined.  Ferrous  iron,  for  example,  may  be  estimated 
by  adding  standard  potassium  permanganate  to  its  acid  solution, 
the  reaction  taking  place  according  to  the  equation  : 

2  KMnO4  -h  ioFeSO4  +  8  H2SO4 

=  5  Fe2(S04)3  +  K2S04  +  2  MnSO4+8  H2O. 

Manganese  dioxide  may  be  determined  by  dissolving  a  weighed 
quantity  in  a  standard  ferrous  sulphate  solution, 

MnO2  +  2  FeSO4  +  2  H2SO4  =  Fe2(SO4)3  +  MnSO4  4-  2  H2O, 

1  Before  taking  up  this  subject  the  student  should  thoroughly  review  the  subject  of 
oxidation  and  reduction,  a  satisfactory  presentation  of  which  will  be  found  in  Tread  well's 
Qualitative  Analysis,  pp.  3—9. 


VOL  UMETRIC  ANAL  YSIS  65 

and  titrating  the  excess  of  ferrous  sulphate  by  means  of  a  standard 
potassium  permanganate  solution  according  to  the  equation  already 
given.  This  last  process  is  an  indirect  method  frequently  used  for 
the  determination  of  substances  of  an  oxidizing  nature.  It  is 
analogous  to  the  method  of  determining  the  purity  of  calcium  car- 
bonate by  dissolving  the  carbonate  in  standard  acid  and  titrating 
the  excess  of  acid  by  means  of  standard  alkali. 

It  is  obvious  that  these  solutions  can  be  standardized  by  titrating 
them  directly  against  the  substance  to  be  determined;  for  example, 
a  solution  of  potassium  permanganate  can  be  standardized  by  titrat- 
ing it  against  a  solution  containing  a  known  amount  of  ferrous 
iron.  In  general,  it  is  advisable  whenever  possible  to  use  this 
method,  since  the  conditions  during  the  standardization  will  then  be 
similar  to  those  existing  during  the  determination,  and  the  results 
will  be  more  accurate.  It  frequently  happens,  however,  that  a 
solution  is  standardized  against  a  substance  other  than  that  to 
be  determined.  For  example,  the  permanganate  solution  can  be 
standardized  against  oxalic  acid  and  employed  to  determine  iron 
and  hydrogen  peroxide. 

Available  Oxygen 

Potassium  permanganate  completely  oxidizes  oxalic  acid  accord- 
ing to  the  equation 

2  KMnO4  +  5  H2C2O4  +  3  H2SO4 

=  K2SO4+2  MnSO4+  ioCO2  +  8  H2O. 

From  the  above  equation  and  that  showing  the  reaction  between 
potassium  permanganate  and  ferrous  sulphate,  it  is  evident  that  all 
of  the  oxygen  in  the  permanganate  is  not  used  for  oxidizing 
purposes.  Two  molecules  of  potassium  permanganate  react  with 
ten  of  ferrous  sulphate.  It  is  apparent  that  of  the  eight  combining 
weights  of  oxygen,  but  five  are  used  for  oxidation.  The  potassium 
permanganate  is  assumed  to  split  up  into  the  oxides  of  the  metals 
(which  in  the  presence  of  acid  form  salts)  with  the  liberation  of 
oxygen,  thus: 


KMnO4 
KMnO 


4  1  =  K2O  +  2  MnO  +  5  O. 

4    J 


That  is,  two    molecules   of   potassium    permanganate    yield   five 

F 


66  QUANTITATIVE  ANALYSIS 

combining  weights  of  oxygen  and  are  said  to  have  five  available 
oxygens.  Therefore,  two  gram  molecules  of  permanganate  (316.6 
grams)  yield  five  combining  weights  (80  grams)  of  oxygen  for 
oxidizing  purposes.  To  make  a  normal  solution  of  permanganate, 
it  is  evident  from  the  definition  that  we  must  have  enough  available 
oxygen  to  react  with  one  combining  weight  of  hydrogen;  i.e., 
eight  grams  of  oxygen  per  liter.  Consequently,  for  a  normal 
solution  we  must  dissolve  in  one  liter  enough  potassium  permanga- 

nate to  furnish  eight  grams  of  available  oxygen  ;  i.e.,  —  of  two 

10 

2  x  158.3 
gram  molecules,  or  -  -  —  -  =  31.66  grams  of  potassium  perman- 

ganate. When  a  potassium  dichromate  solution  is  employed  as 
an  oxidizing  agent,  it  is  assumed  to  break  down  into  the  oxides  of 
the  metals  (which  in  the  presence  of  acids  form  salts)  with  the 
liberation  of  oxygen.  The  process  may  be  represented  as  follows  : 

K2Cr207  =  K20  +  2  Cr08. 


Consequently,  from  one  gram  molecule  of  potassium  dichromate 
three  combining  weights  of  oxygen  (48  grams)  are  available  for 
oxidizing  purposes.  For  a  normal  solution,  therefore,  ^(3  O  =  6  H) 
of  one  gram  molecule  of  potassium  dichromate  should  be  taken 
for  a  liter  of  solution. 

Some  of  the  principal  oxidizing   and   reducing  agents  used  in 
volumetric  processes  are  : 

Potassium  permanganate 
Potassium  dichromate 
Potassium  bromate 

Oxidizing  Agents  J  Potfsium  iodate 

Hydrogen  peroxide 

Chlorine 
Bromine 
Iodine 


VOLUMETRIC  ANALYSIS  67 

Hydrogen  (obtained  from  the  action 

of  acid  on  zinc) 
Sulphurous  acid 
Oxalic  acid 


Reducing  Agents 


Stannous  chloride 
Ferrous  sulphate 
Arsenious  oxide 
Sodium  thiosulphate 
Hydrogen  sulphide 


THE   PERMANGANATE   METHOD 

Solutions  of  potassium  permanganate  are  intensely  colored,  but 
on  being  reduced  a  colorless  solution  is  formed.  A  slight  excess 
of  permanganate  gives  the  solution  a  pink  color,  so  that  on  reach- 
ing the  end  point  the  permanganate  acts  as  its  own  indicator. 

Potassium  permanganate  may  be  obtained  pure,  but  since  the 
strength  of  the  solution  changes  when  first  prepared,  it  should 
always  be  standardized.  This  may  be  done : 

a.  By  means  of  pure  electrolytic  iron  dissolved  in  sulphuric  acid 
out  of  contact  with  the  air. 

b.  By  means  of  pure  iron,  dissolved  in  acid  and  reduced  to  the 
ferrous  state  by  means  of  zinc. 

c.  Against  pure  ferrous  ammonium  sulphate  (Mohr's  Salt). 

d.  Against  pure  sodium  oxalate. 

EXERCISE  XVIII 
Preparation  of  a  Solution  of  Potassium  Permanganate 

Procedure.  —  Calculate  the  amount  of  potassium  permanganate 
necessary  to  make  one  liter  of  a  solution  of  such  strength  that 
20  c.c.  would  be  required  to  furnish  the  oxygen  necessary  to  oxi- 
dize o.i  gram  of  pure  iron  from  the  ferrous  to  the  ferric  state. 
Weigh  out  approximately  this  amount,  place  it  into  a  No.  8  beaker, 
and  dissolve  in  one  liter  of  water.  Allow  the  solution  to  stand  for  a 
few  hours,  and  filter  through  a  layer  of  asbestos  free  from  organic 
matter  into  a  two-liter  glass-stoppered  bottle.  The  asbestos  filter 
may  be  prepared  by  placing  a  few  short  pieces  of  glass  tubing 
into  a  Gooch  funnel,  and  upon  this  a  thin  layer  of  asbestos  fiber. 


68  QUANTITATIVE  ANALYSIS 

Suction  may  be  used  to  hasten  the  filtration.     Keep  the  solution 
in  a  dark  place  when  not  in  use. 

Notes.  —  i.  Distilled  water  contains  small  amounts  of  ammonium 
hydroxide  and  organic  matter,  which  decompose  the  permanganate 
with  the  separation  of  manganese  dioxide.  It  is  well  to  allow  the 
permanganate  solution  to  stand  some  time  in  order  that  these  sub- 
stances may  be  completely  oxidized.  The  presence  of  even  small 
quantities  of  manganese  dioxide  decomposes  the  permanganate, 
with  the  separation  of  more  of  this  substance.  It  is  necessary 
therefore  to  remove  the  dioxide  by  filtration  and  to  keep  the  solu- 
tion out  of  contact  with  dust  and  any  other  organic  matter  which 
would  reduce  it. 

2.  If  potassium  permanganate  solution  is  kept  out  of  the  light 
and  free  from  organic  matter,  its  strength  will  remain  unchanged 
for  months. 

3.  The  solution  prepared  as  above  is  approximately  tenth-nor- 
mal.    Stronger  solutions  of  potassium  permanganate  are  seldom 
employed. 

EXERCISE  XIX 

Standardization  of  a  Solution  of  Potassium  Permanganate 

a.   By  Means  of  Pure  Iron  dissolved  out  of  Contact  with  Air 

Procedure.  —  Weigh  out  three  portions  of  electrolytic  iron  of 
about  o.i  gram  each.  Dissolve  out  of  contact  with  the  air  in  the 
following  manner :  Provide  three  Erlenmeyer  flasks  with  well  fit- 
ting stoppers,  carrying  bent  glass  tubes,  as  illustrated  in  Fig.  18. 
One  end  of  the  tube  should  extend  about  0.5  cm.  below  the  cork. 
When  the  cork  carrying  the  tube  is  in  place,  the  other  end  of  the 
tube  should  reach  nearly  to  the  bottom  of  a  beaker  containing  a 
five  per  cent  solution  of  sodium  bicarbonate.  Add  to  each  flask 
about  30  c.c.  of  dilute  sulphuric  acid,  then  add  a  piece  of  sodium 
bicarbonate  about  the  size  of  a  small  pea  for  the  purpose  of  expel- 
ling the  oxygen  in  the  flask.  Immediately  introduce  one  of  the 
weighed  portions  of  iron  into  each  flask,  insert  the  stopper,  and 
warm  gently.  When  the  iron  has  all  dissolved,  remove  the  stop- 
per, dilute  with  about  50  c.c.  of  distilled  water,  and  add  perman- 
ganate from  the  glass-stoppered  burette  to  the  cold  solution  until 
a  faint  pinkish  tint  is  produced  which  remains  for  one  minute. 
(Use  the  upper  edge  of  the  meniscus  when  reading  the  burette.) 


VOLUMETRIC  ANALYSIS  69 

From  the  data  obtained  calculate  the  value  of  one  cubic  centi- 
meter of  the  permanganate  solution  in  terms  of  iron.  Also,  cal- 
culate the  amount  of  oxygen  (in  grams)  available  for  oxidizing 
purposes  in  one  cubic  centimeter  of  the  permanganate  solution. 
These  results  of  the  standardization  should  agree  within  two-tenths 
per  cent  of  the  total  amount  of 
oxygen  present.  For  method  of 
calculation  see  page  184. 

Notes.  —  i .  Sulphuric  acid  must 
be  used  for  dissolving  the  iron,  as 
hydrochloric  acid  reacts  with  the 
permanganate,  liberating  chlorine. 
It  is  possible,  however,  to  titrate 
the  iron  in  the  presence  of  hydro- 
chloric acid,  if  the  solution  con- 
tains a  large  excess  of  manganese 
sulphate.  Upon  this  fact  is  based 

the    Zimmerman-Reinhardt   method    described    in    the  Jour.  Am. 
Cheni.  Soc.,  17,  405  (1895). 

2.  The  soft  iron  wire  sometimes  recommended  for  this  method 
of  standardization  should  not  be  used.     It  contains  carbonaceous 
matter,  which  is  liberated  when  the  iron  is  dissolved  in  acid,  with  the 
result  that  some  of  the  permanganate  is  used  to  oxidize  the  hydro- 
carbons formed  and  high  results  are  obtained  when  expressed  in 
terms  of  iron. 

3.  Electrolytic  iron  which  has  not  been  annealed  dissolves  very 
readily  in  acids. 

4.  Since   permanganate    solutions    attack    organic   matter,    the 
glass-stoppered  burettes  must  always  be  used. 

5.  The  formation  of  a  brown  turbidity  or  precipitate  during  the 
titration  indicates  insufficient  acid.     It  consists    of  the  oxides  of 
manganese. 

b.    By  Pure  Iron  reduced  by  Means  of  a  Jones  Redtictor 

In  this  method  the  iron  is  dissolved  in  acid  and  reduced  to  the 
ferrous  state  by  running  the  solution  through  a  tube  containing 
granulated  zinc.  The  zinc  is  amalgamated  to  prevent  its  being 
consumed  too  rapidly. 

The  tube  containing  the  zinc  is  known  as  the  Jones  Reductor. 


QUANTITATIVE  ANALYSIS 


This  is  illustrated  in  Fig.  19.  The  large  tube  has  an  outside  di- 
ameter of  about  three  quarters  of  an  inch.  At  the  bottom  of  this 
are  placed  some  glass  beads  upon  which  rest  a  layer  of  glass 
wool,  then  a  thin  layer  of  asbestos,  and  a  column  of  amalgamated 
zinc  about  ten  inches  in  length.  Upon  the  zinc  is 
\/  placed  a  layer  of  glass  wool  about  two  inches  in 
length.  The  zinc  should  be  of  such  size  that  it  will 
pass  through  a  20  mesh,  but  not  through  a  30  rmesh 
sieve.  It  is  best  amalgamated  by  the  method  given 
by  Lord.1  Moisten  a  quantity  of  the  zinc  with  dilute 
sulphuric  acid  (about  3  c.c.  concentrated  acid  to  100 
c.c.  of  water),  add  a  small  drop  of  mercury,  and  stir 
until  the  zinc  shows  uniformly  the  white  mercury 
color.  Avoid  an  excess  of  mercury.  One  half  gram 
is  sufficient  for  150  grams  of  zinc.  Wash  the  zinc 
free  from  acid  and  put  it  into  the  tube. 


Determination  of  the  Blank 

Since  the  reagents  after  passing  through  the  reduc- 
tor  will  almost  invariably  consume  some  permanga- 
nate due  to  impurities  in  the  zinc,  etc.,  blank 
determinations  should  be  made  until  concordant 
results  are  obtained. 

Connect  the  reductor  with  the  filter  pump,  using 
an  intervening  Wolff  bottle  to  prevent  the  water  from 
the  tap  running  back  into  the  flask.  Run  through  the  tube  about 
300  c.c.  of  hot  (7O°-8o°)  dilute  sulphuric  acid  (about  50  c.c.  of 
concentrated  sulphuric  acid  in  a  liter)  by  filling  the  funnel,  turn- 
ing on  the  suction,  and  opening  the  stopcock  wide  enough  to 
allow  the  acid  to  run  into  the  filter  flask  at  a  rate  not  greater 
than  40  c.c.  per  minute.  Be  sure  to  leave  the  funnel  partially 
filled.  Follow  the  acid  with  100  c.c.  of  distilled  water,  leaving 
a  little  in  the  funnel.  Titrate  the  solution  in  the  filter  flask 
with  the  potassium  permanganate.  Repeat  the  above  operation 
until  two  consecutive  blanks  check. 


FIG.  19 


1  Lord,  Notes  on  Metallurgical  Analysis,  p.  36  (1903). 


VOLUMETRIC  ANALYSIS  71 

Reduction  and  Titration  of  the  Iron 

Procedure.  —  Weigh  out  into  No.  3  beakers  three  portions  of  iron 
of  about  o.i  gram  each.  Dissolve  them  in  about  100  c.c.  of  dilute 
sulphuric  acid,  of  the  concentration  used  in  the  blank  determi- 
nation. Pour  the  hot  solution  through  the  reductor  at  a  rate  not 
exceeding  40  c.c.  per  minute,  follow  it  with  200  c.c.  of  the  warm 
dilute  sulphuric  acid,  some  of  which  should  be  used  to  rinse  out 
the  beaker  containing  the  solution  of  iron,  and  then  with  100  c.c. 
of  distilled  water.  Cool  the  solution  and  titrate  in  the  filter  flask 
with  the  permanganate  solution.  Deduct  the  blank  from  the 
amount  of  permanganate  used  and  from  the  data  calculate  the 
value  of  permanganate  in  terms  of  iron  and  also  the  available 
oxygen  per  cubic  centimeter. 

Note.  —  Besides  zinc,  sulphur  dioxide  and  hydrogen  sulphide 
may  be  used  to  reduce  the  iron  to  the  ferrous  condition.  The 
excess  of  these  reducing  agents,  however,  must  be  removed  from 
the  solution  before  titration,  by  means  of  a  current  of  carbon  dioxide. 
Zinc  has  the  disadvantage  of  always  containing  a  certain  amount 
of  iron. 

c.    By  Ferrous  Ammonium  Sulphate 
(FeSO4(NH4)2SO4  -  6  H2O) 

Procedure.  —  Weigh  out  upon  cover-glasses  three  separate  por- 
tions of  pure  ferrous  ammonium  sulphate  of  about  0.7  gram  each. 
Place  about  25  c.c.  of  water  and  15  c.c.  of  dilute  sulphuric  acid 
into  each  of  three  Erlenmeyer  flasks,  add  a  piece  of  sodium  bicar- 
bonate the  size  of  a  small  pea,  and  immediately  introduce  one  por- 
tion of  the  ferrous  ammonium  sulphate  into  each  flask.  When  all 
of  the  substance  has  dissolved,  titrate  with  the  permanganate  as  in 
the  previous  methods  of  standardization.  Calculate  the  number 
of  grams  of  available  oxygen  per  cubic  centimeter  of  perman- 
ganate solution,  also  the  value  of  one  cubic  centimeter  of  the  per- 
manganate in  terms  of  iron. 

Notes. —  i.  Ferrous  ammonium  sulphate  may  be  obtained  very 
pure  by  recrystallization,  and  is  a  very  satisfactory  substance  to 
use  for  the  standardization  of  permanganate. 

2.  In  the  presence  of  an  excess  of  sulphuric  acid  ferrous  sul- 
phate is  oxidized  but  very  slowly  by  the  oxygen  of  the  air. 


72  QUANTITATIVE  ANALYSIS 

d.    By  Means  of  Sodium  Oxalate 
(Na2C204) 

Principle.  —  Sodium  oxalate  on  being  dissolved  in  water  and 
acidified  with  sulphuric  acid  can  be  titrated  with  potassium  per- 
manganate solution : 

5  Na2C2O4  +  2  KMnO4  +  8  H2SO4 

=  5  Na2SO4  +  K2SO4  +  2  MnSO4  +  8  H2O. 

The  solution  must  be  heated  to  about  70°,  as  the  reaction  takes 
place  very  slowly  at  the  ordinary  temperature. 

Procedure.  —  Weigh  out  about  one  gram  of  the  sodium  oxalate, 
dissolve  in  about  100  c.c.  of  hot  water,  transfer  to  a  250  c.c.  flask, 
cool,  and  make  up  to  the  mark.  Run  into  an  Erlenmeyer  flask 
about  25  c.c.  of  the  oxalate  solution,  add  10  c.c.  of  dilute  sulphuric 
acid,  heat  to  about  70°,  and  titrate  with  the  permanganate  solution 
until  the  solution  assumes  a  pink  tint  that  remains  for  a  few 
minutes.  Repeat  the  titration  until  concordant  results  are  ob- 
tained. Calculate  the  value  of  one  cubic  centimeter  of  the  per- 
manganate solution  in  terms  of  iron  and  .also  the  available  oxygen 
per  cubic  centimeter. 

Note.  —  Potassium  permanganate  may  also  be  standardized 
against  other  oxalates  or  oxalic  acid.  Many  of  these  compounds 
contain  water  of  crystallization,  a  part  of  which  may  easily  be  lost. 
Pure  sodium  oxalate  may  be  readily  prepared  and  kept,  and  is  an 
excellent  substance  for  standardizing  the  permanganate.  The 
method  of  preparing  pure  sodium  oxalate  is  described  by  Sorensen, 
Zeit.  fiir  Anal.  Chem.,  36,  639  (1897). 

|  ! 
EXERCISE  XX 

Determination  of  the  Percentage  Purity  of  Oxalates 
One  of  the  following  oxalates  may  be  analyzed  :  — 

Potassium  oxalate  ....  K2C2O4  •  H2O 

Ammonium  oxalate        .         .         .         .  (NH4)2C2O4  •  H2O 

Potassium  acid  oxalate  ....  KHC2O4  •  H2O 

Potassium  tetra  oxalate          .         .         .  KH3(C2O4)2  •  2H2O 


VOLUMETRIC  ANALYSIS  73 

Procedure.  —  Weigh  out  from  two  to  three  grams  of  the 
sample,  dissolve  in  hot  water,  and  make  up  to  a  volume  of  250  c.c. 
Titrate  portions  of  the  solution  as  in  the  standardization  of  the 
permanganate  by  means  of  sodium  oxalate. 

Calculate  the  percentage  purity  of  the  substance  analyzed. 

EXERCISE  XXI 
Determination  of  the  Purity  of  Hydrogen  Peroxide 

Principle.  —  This  determination  is  based  upon  the  fact  that  in 
an  acid  solution  hydrogen  peroxide  reacts  with  permanganate 
with  the  evolution  of  oxygen  according  to  the  equation : 

2  KMnO4  +  5  H2O2+3  H2SO4=  K2SO4  +  2  MnSO4  +  8  H2O+  5  O2. 

Procedure.  —  Introduce  10  c.c.  of  the  peroxide  solution  into  a 
250  c.c.  graduated  flask,  make  up  to  the  mark,  and  mix  thoroughly. 
Measure  out  25  c.c.  of  this  solution  into  an  Erlenmeyer  flask, 
dilute  to  100  c.c.,  add  10  c.c.  of  dilute  sulphuric  acid,  and  titrate 
with  the  standard  permanganate  until  a  faint  pinkish  tint  remains. 
Repeat  until  the  ratio  between  the  two  solutions  is  established. 
From  the  data  calculate  the  percentage  purity  of  the  sample, 
assuming  the  specific  gravity  to  be  one.  Calculate  also  the  avail- 
able oxygen  in  one  cubic  centimeter  of  the  sample. 

EXERCISE  XXII 
Determination  of  Calcium 

Principle. — The  calcium  is  precipitated  as  the  oxalate  and 
dissolved  in  dilute  sulphuric  acid  according  to  the  equation : 

CaC2O4  +  H2SO4  =  CaSO4  +  H2C2O4. 

By  titrating  the  oxalic  acid  with  a  standard  permanganate  solution, 
the  amount  of  calcium  present  can  be  determined. 

Procedure.  —  Weigh  out  from  one  to  two  grams  of  the  sample, 
dissolve  in  a  covered  beaker  in  hydrochloric  acid,  and  heat  to  drive 
off  the  carbon  dioxide.  Transfer  to  a  250  c.c.  graduated  flask 
and  make  up  to  the  mark.  Take  two  portions  of  TOO  c.c.  each, 
and  precipitate  the  calcium  as  described  in  Exercise  VII.  After 
washing  the  precipitate  free  from  ammonium  oxalate,  place  the 


74  QUANTITATIVE  ANALYSIS 

beaker  in  which  it  was  precipitated  under  the  funnel  and  dissolve 
the  oxalate  by  pouring  upon  the  filter  30  c.c.  of  dilute  sulphuric 
acid.  Wash  the  filter  finally  with  boiling  water.  Titrate  the  hot 
solution  of  oxalic  acid  with  the  standard  permanganate  solution. 
From  the  data  calculate  the  percentage  of  calcium  oxide  in  the 
sample  taken  for  analysis. 

Note.  —  The  wash  water  from  the  calcium  oxalate  may  be 
tested  for  ammonium  oxalate  by  acidifying  a  few  cubic  centi- 
meters, and  adding  to  the  hot  solution  a  drop  of  very  dilute  per- 
manganate solution.  If  the  color  is  not  discharged,  the  washing 
is  complete. 

EXERCISE  XXIII 
Determination  of  Iron  in  Siderite 

Procedure. — Weigh  out  into  porcelain  crucibles  three  portions 
of  the  finely  ground  sample  of  about  0.25  gram  each.  Heat  the 
crucibles  in  the  hottest  flame  of  an  ordinary  burner  for  about  ten 
minutes.  Cool,  transfer  the  contents  of  the  crucibles  to  250  c.c. 
casseroles,  cover  with  a  cover-glass,  add  10  c.c.  of  concentrated 
hydrochloric  acid,  and  heat  until  the  iron  is  in  solution.  Elevate 
the  cover-glass  by  means  of  a  glass  triangle  (see  Fig.  5),  add 
20  c.c.  of  sulphuric  acid  (sp.  gr.  1.4),  and  heat  until  the  dense 
white  fumes  of  sulphuric  acid  begin  to  be  evolved.  Cool  the 
solution,  dilute  to  100  c.c.,  heat  to  dissolve  any  iron  salts,  and  run 
the  hot  solution  through  a  clean  Jones  reductor  as  in  the  stand- 
ardization of  the  permanganate.  A  white  flocculent  residue  may 
be  disregarded,  as  it  is  silica,  and  will  be  removed  by  the  glass 
wool  in  the  reductor.  Wash  the  reductor  with  200  c.c.  of  the 
warm  dilute  sulphuric  acid  (50  c.c.  concentrated  acid  in  one  liter) 
and  100  c.c.  of  distilled  water.  Titrate  the  cold  solution  with  per- 
manganate and  calculate  the  percentage  of  iron,  also  the  percent- 
age of  ferrous  oxide  in  the  sample  taken  for  analysis. 

Notes.  —  i.  Siderite  is  a  native  carbonate  of  iron,  containing 
silica,  organic  matter,  and  various  other  impurities.  Since  the 
organic  matter  would  consume  some  of  the  permanganate,  it  must 
be  destroyed  by  heating  (roasting). 

2.  Iron  ores  frequently  contain  appreciable  quantities  of  tita- 
nium. In  this  case  a  certain  amount  of  the  titanium  is  dissolved, 


VOLUMETRIC  ANALYSIS  75 

and  is  partly  reduced  by  the  zinc  from  the  oxide  TiO2  to  Ti2O3. 
On  titrating  the  latter  compound,  it  consumes  some  of  the  per- 
manganate, being  changed  back  to  TiO2.  It  is  obvious,  there- 
fore, that  when  titanium  is  present  zinc  cannot  be  used  for  the 
reduction  of  the  iron. 

THE   BICHROMATE   METHOD 

This  method  depends  upon  the  fact  that  in  acid  solutions 
ferrous  salts  can  be  completely  oxidized  by  dichromate  solutions, 
the  reaction  taking  place  according  to  the  equation  : 

K2Cr2O7  +  6  FeCl2  +  14  HC1  =  6  FeCl3  +  2  Cr2Cl3+  2  KC1  +  7  H2O. 

Potassium  dichromate  does  not  react  with  the  hydrochloric  acid 
present,  consequently  it  may  be  used  in  this  class  of  analyses. 

The  complete  reduction  of  the  iron  to  the  ferrous  condition  is 
accomplished  by  the  addition  of  an  excess  of  stannous  chloride 
(2  FeCl3  +  SnCl2  =  2  FeCl2  +  SnCl4).  As  the  excess  of  the  stan- 
nous chloride  would  react  with  the  dichromate,  it  is  oxidized  by 
the  addition  of  an  excess  of  mercuric  chloride  solution,  according 
to  the  following  equation  : 

SnCl2  +  2  HgCl2  =  SnCl4  +  2  HgCl. 

The  mercurous  chloride  forms  a  white  precipitate  which  is  not 
oxidized  by  the  dichromate.  If  a  large  excess  of  the  stannous 
chloride  is  present,  and  if  the  solution  is  warm,  a  grayish  precipi- 
tate composed  largely  of  mercury  may  be  formed. 

SnCl2  +  HgCl2  =  SnCl4  +  Hg. 

Since  the  mercury  is  oxidized  by  the  dichromate,  these  conditions 
must  be  avoided. 

When  the  dichromate  is  reduced  according  to  the  equation  given 
above,  the  solution  turns  green  from  the  formation  of  chromic 
chloride.  This  prevents  the  determination  of  the  end  point  by 
placing  an  indicator  in  the  solution.  It  is  necessary,  therefore, 
to  remove  drops  of  the  solution  and  bring  them  into  contact  with 
the  indicator  outside  of  the  solution.  Potassium  ferricyanide 
(K3Fe(CN)6),  which  gives  a  blue  color  (Turnbull's  blue)  with 
ferrous  salts,  is  employed  as  the  indicator. 


76  QUANTITATIVE  ANALYSIS 

Preparation  of  the  Bichromate  Solution 

Obtain  a  sample  of  pure  potassium  dichromate  and  calculate 
the  amount  necessary  to  make  a  liter  of  a  solution  of  such  strength 
that  20  c.c.  will  oxidize  o.i  gram  of  iron.  Weigh  out  this  amount 
approximately,  dissolve  in  water,  and  make  up  to  one  liter.  The 
solution  will  keep  indefinitely  without  changing. 

Note. — The  dichromate  may  also  be  weighed  out  accurately,  as 
it  can  be  prepared  very  pure. 

The  Indicator 

Dissolve  a  piece  of  pure  potassium  ferricyanide  about  the  size 
of  the  head  of  a  pin  in  about  20  c.c.  of  water. 

Notes. — i.  The  solution  must  be  prepared  fresh,  as  it  is  reduced 
on  standing.  It  must  be  dilute,  or  its  own  color  will  interfere  with 
the  end  point. 

2.  Potassium  ferricyanide  which  is  free  from  ferrocyanide  must 
be  used,  as  this  compound  reacts  with  ferric  iron  with  the  for- 
mation of  a  blue  color. 

EXERCISE  XXIV 
Standardization  of  the  Solution  of  Potassium  Dichromate 

a.  Against  Ferrous  Ammonium  Sulphate 

Procedure. — Weigh  out  three  portions  of  the  pure  salt  of  about 
0.7  gram  each  and  dissolve  them  in  flasks  containing  100  c.c.  of 
water  and  10  c.c.  of  concentrated  hydrochloric  acid.  The  air 
should  be  expelled  from  the  flask  by  means  of  a  small  piece  of 
sodium  bicarbonate  as  in  the  standardization  of  the  permanganate. 
The  ferrous  ammonium  sulphate  is  very  nearly  one-seventh  iron. 
Hence,  if  exactly  0.7  gram  were  weighed  out,  this  would  be  the 
equivalent  of  o.i  gram  Fe  and  20  c.c.  of  the  solution  would  be 
used  in  the  titration.  Introduce  into  the  flask  one  cubic  centime- 
ter less  than  the  calculated  amount  of  the  dichromate  necessary  to 
oxidize  the  iron  in  the  sample,  stir  well,  then,  by  means  of  a  stir- 
ring rod,  bring  as  small  a  drop  of  the  solution  as  possible  next  to 
a  drop  of  the  ferricyanide  indicator  which  has  been  placed  on  a 
white  porcelain  tile  or  titration  plate,  and  allow  the  two  drops  to 


VOL  UMETRIC  ANAL  YSIS  77 

run  together.  A  blue  coloration  at  the  junction  of  the  two  drops 
indicates  the  presence  of  ferrous  iron,  and  that  not  enough  of  the 
dichromate  solution  has  been  introduced  to  oxidize  the  iron.  Add 
a  few  drops  more  of  the  dichromate  solution,  and  with  a  clean  stir- 
ring rod  test  for  the  presence  of  ferrous  iron  as  just  described. 
When  near  the  end  point,  a  pale  blue  color  will  be  developed. 
Now  add  the  dichromate  a  drop  at  a  time,  until  a  point  is  reached 
when  no  color  can  be  seen,  after  the  solution  stands  for  one  minute. 
Read  the  burette  and  from  the  data  calculate  the  value  of  one  cu- 
bic centimeter  of  the  dichromate  solution  in  terms  of  iron  and  also 
of  the  available  oxygen. 

Note. — The  formation  of  a  brown  precipitate  on  bringing  the 
solution  and  the  indicator  together  shows  that  the  solution  of  the 
indicator  is  too  concentrated. 

b.   Against  Pure  Iron 

Procedure.  —  Dissolve  three  accurately  weighed  portions  of  pure 
iron  of  about  o.  I  gram  each  by  placing  into  Erlenmeyer  flasks 
containing  25  c.c.  of  concentrated  hydrochloric  acid  and  heating. 
Add  to  the  hot  solution  stannous  chloride  solution  drop  by  drop 
until  one  drop  causes  the  liquid  to  become  colorless.  Dilute  with 
100  c.c.  of  distilled  water  and  to  the  cold  solution  add  25  c.c.  of 
mercuric  chloride  solution  and  stir.  A  white  precipitate  should 
form.  In  case  the  precipitate  is  gray,  discard  the  solution. 
After  three  or  four  minutes,  titrate  the  solution  with  the  dichro- 
mate in  the  manner  already  described.  Calculate  the  value  of  one 
cubic  centimeter  of  the  dichromate  in  terms  of  iron  and  of  avail- 
able oxygen. 

Note.  —  Zinc  cannot  be  used  for  the  reduction  in  this  case,  as  it 
would  form  an  insoluble  white  precipitate  with  the  ferricyanide 
and  obscure  the  end  point. 

EXERCISE  XXV 
Determination  of  Iron  in  Siderite 

Procedure.  —  Weigh  out  the  samples  and  roast  as  described  un- 
der Exercise  XXIII.  Dissolve  in  hydrochloric  acid,  reduce,  and 
titrate  with  potassium  dichromate  solution  as  just  described. 
Calculate  the  percentage  of  iron  present;  also,  of  ferrous  oxide. 


78  QUANTITATIVE  ANALYSIS 

Note.  —  The  dichromate  method  finds  frequent  application  in  the 
analysis  of  iron  ores,  since  hydrochloric  acid  is  the  best  solvent 
for  this  class  of  ores. 

IODIMETRY 

In  neutral  or  acid  solutions  iodine  is  an  indirect  oxidizing  agent. 
In  the  presence  of  a  reducing  agent  it  may  be  assumed  to  react 
with  the  water  present  and  liberate  oxygen  for  the  oxidation.  For 
example,  sulphurous  acid  is  oxidized  by  iodine  according  to  the 
equation : 

Na2SO3  +  I2  +  H2O  =  Na2SO4  +  2.  HI. 

Iodine  cannot  be  used  in  the  presence  of  caustic  alkalies  or  the 
normal  carbonates  as  it  reacts  with  these  substances.  Its  use  in 
alkaline  solutions  is  made  possible  by  the  fact  that  it  does  not  re- 
act with  the  bicarbonate ;  consequently,  this  substance  is  used  in 
making  determinations  which  must  be  carried  out  in  alkaline  solu- 
tions. The  indicator  used  in  determinations  of  this  kind  is  starch, 
which  in  solution  forms  a  blue  compound  with  iodine. 

The  methods  of  determination  in  iodimetry  may  be  divided  into 
three  general  classes: 

1.  The    titration  of  oxidizable    bodies,    i.e.,  reducing    agents. 
The  titration  of  an  antimonous  compound  serves  as  an  illustration. 

Na3SbO3  +  I2  +  2  NaHCO3  =  Na3SbO4  +  2  Nal  +  H2O  +  2CO2. 

2.  Bodies  which  contain  available  oxygen,  i.e.,  oxidizing  agents. 
In  this  class  of  reactions,  iodine  is  set  free  and  may  be  titrated 
by  means  of  a  suitable  reagent. 

H202  +  2  KI  +  H2S04  =  I2  +  K2S04  +  2  H20. 

The  iodine  liberated  is  titrated  direct  by  a  standard  reducing 
agent.  For  this  purpose,  a  solution  of  sodium  thiosulphate  may 
be  employed,  which  is  oxidized  by  means  of  iodine  to  the  sodium 
salt  of  tetrathionic  acid. 

2  Na2S2O3  +  I2  =  Na2S4O6  +  2  Nal. 

3.  Free  chlorine  or  compounds  which  can  liberate  this  substance. 
In  methods   of  this   class   the  chlorine  is    brought  into    contact 
with  potassium  iodide  solutions,  iodine  being  set  free  according  to 
the  equation : 

C12  +  2  KI  =  2  KC1  +  I2- 


VOLUMETRIC  ANALYSIS  79 

The   iodine   may    then    be    titrated   with    standard    thiosulphate 
solution. 

From  the  equation  which  represents  the  oxidation  of  sulphurous 
acid,  H2SO3  +  I2  +  H2O  =  H2SO4  +  2  HI,  it  is  evident  that  one 
molecule  of  iodine  (I2)  furnishes  one  combining  weight  of  oxygen 
for  the  oxidation  of  the  sulphurous  acid.  One  combining  weight 
of  iodine  (126.97  grams)  would  consequently  be  equal  to  8  grams 
of  oxygen  and,  therefore,  equivalent  to  a  combining  weight  of 
hydrogen.  A  normal  solution  of  iodine,  therefore,  contains  one 
combining  weight  of  iodine  per  liter.  Since  one  gram  molecule  of 
sodium  thiosulphate  (248.3  grams)  reacts  with  one  combining 
weight  of  the  iodine,  a  normal  solution  of  the  thiosulphate  will 
contain  248.3  grams  in  a  liter. 

EXERCISE  XXVI 
Preparation  of  Solutions 

a.  Approximately    N/io    Iodine     Solution.  —  Weigh     approxi- 
mately 6.3  grams  of  resub limed  iodine  into  a  No.  3  beaker.     Place 
into  the  beaker  about  10  grams  of  potassium  iodide.     Mix  it  with 
the  iodine  and  dissolve  in  as  little  water  as  possible.     Transfer  to 
a  half  liter  graduated  flask  and  make  up  to  the  mark. 

Notes. —  i.  Iodine  is  very  slightly  soluble  in  water.  It  dissolves 
in  a  solution  of  potassium  iodide,  forming  KI3,  which  is  easily  de- 
composed with  the  formation  of  potassium  iodide  and  iodine  which 
is  available  for  oxidation. 

2.  The  iodine  solution  changes  on  standing,  especially  if  exposed 
to  the  light.    Hydriodic  acid  is  one  of  the  products  of  decomposition. 

3.  Iodine  attacks  organic  matter,   consequently  the  glass-stop- 
pered burette  must  always  be  used. 

b.  N/lQ  Sodium  Thiosulphate  Solution. — Weigh  into  a  No.  I 
tared  beaker  exactly   24.83   grams  of  pure  recrystallized  sodium 
thiosulphate  (Na2S2O3  •  5  H2O).     Dissolve  it  in  water  which  has 
been  boiled  to  expel  the  air,  transfer  to  a  liter  flask,  and  make  up 
to  the  mark  with  the  boiled  distilled  water. 

Note. — If  made  up  under  these  conditions  the  thiosulphate  will 
remain  unchanged  for  months.  The  presence  of  carbon  dioxide 
in  the  solution  decomposes  the  thiosulphate  with  the  separation  of 
sulphur. 


80  QUANTITATIVE  ANALYSIS 

c.  Starch  Solution.  —  Make  a  paste  by  grinding  about  one  gram 
of  starch  in  a  mortar  with  5  c.c.  of  water.  Pour  this  into  200  c.c. 
of  boiling  water  and  stir  well.  Allow  to  settle  and  decant  the 
clear  liquid,  which  is  to  be  used  in  the  subsequent  titrations.  Use 
about  2  c.c.  for  each  titration. 

Notes.  —  i.  The  solution  does  not  keep  well.  Moulds  grow  in 
it,  and  starch  is  split  up  into  dextrin  and  other  carbohydrates,  some 
of  which  give  reddish-colored  solutions  with  the  iodine.  It  is  best 
to  prepare  a  fresh  solution  each  day. 

2.  A  form  of  starch  which  is  soluble  in  water  and  known  as 
soluble  starch  may  conveniently  be  used  for  the  preparation  of  the 
indicator. 

EXERCISE   XXVII 

Standardization  of  the  Iodine  Solution 

This  may  be  done  : 

Directly,  by  titrating  against  solutions  of  thiosulphate  or  arse- 
nious  oxide  of  known  strength ; 

Indirectly,  by  titrating  the  iodine  with  thiosulphate  solution  and 
standardizing  the  thiosulphate  by  means  of  an  oxidizing  agent  of 
known  strength.  By  using  pure  thiosulphate  for  the  standard 
solution,  a  double  check  on  the  iodine  solution  is  obtained. 


a.    Standardization  of  the  Iodine  Solution  against 
Thiosulphate 

Procedure.  —  Place  some  of  the  iodine  solution  into  the  burette 
with  the  glass  stopcock,  and  fill  the  pinchcock  burette  with  the 
thiosulphate  solution.  Run  into  an  Erlenmeyer  flask  about  25  c.c. 
of  the  thiosulphate  solution,  add  about  2  c.c.  of  the  starch  solu- 
tion, dilute  with  50  c.c.  of  water,  then  titrate  with  the  iodine  solu- 
tion until  a  blue  coloration  just  appears.  Repeat  this  until  the 
ratio  is  established  between  the  two  solutions.  Express  the  ratio 
in  terms  of  one  cubic  centimeter  of  the  thiosulphate  solution. 
Calculate  the  grams  of  iodine  per  cubic  centimeter  of  the  iodine 
solution. 

b.    Against  7V/IO  Arsenious  Oxide  Solution 

Principle.  —  This  method  depends  upon  the  fact  that  in  an 
alkaline  solution  sodium  arsenite  may  be  titrated  with  iodine 
solution  according  to  the  equation : 

N", AsO3  +  I2  +  2  NaHCO3  =  Na3AsO4  +  2  Nal  +  2  CO2  +  H2O. 


VOL  UME  TRIG  ANAL  YS1S  8  1 

Procedure.  —  Weigh  2.475  grams  of  pure  arsenious  oxide  into 
a  No.  3  beaker.  Dissolve  in  the  least  possible  amount  of  warm 
10  per  cent  sodium  hydroxide  solution.  Wash  the  contents  of  the 
beaker  into  a  500  c.c.  measuring  flask,  add  a  drop  of  phenolphtha- 
lein,  then  add  dilute  hydrochloric  acid  until  the  solution  is  color- 
less. Dissolve  about  10  grams  of  pure  sodium  bicarbonate  in  a 
little  water,  filter  if  necessary,  and  add  the  solution  to  the  contents 
of  the  flask.  If  the  solution  is  alkaline,  add  a  few  drops  of  the 
dilute  acid  until  it  is  decolorized.  Make  the  solution  up  to  the 
mark  with  distilled  water.  Titrate  portions  of  this  solution  against 
the  standard  iodine  solution  until  the  ratio  is  established.  From 
the  data  calculate  the  number  of  grams  of  iodine  in  each  cubic 
centimeter  of  the  iodine  solution. 

Notes.  —  i.  Arsenious  oxide  is  much  more  easily  soluble  in 
sodium  hydroxide  solution  than  in  a  solution  of  the  bicarbonate. 
From  what  has  already  been  said,  it  is  evident  that  the  excess  of 
caustic  alkali  must  be  removed.  This  is  done  by  neutralizing  with 
acid.  Since  the  titration  must  be  carried  out  in  an  alkaline  solu- 
tion an  excess  of  sodium  bicarbonate  is  then  added. 

2.  The  reaction  between  arsenious  oxide  and  iodine  takes  place 
in  acid  solution.  Under  these  conditions,  however,  the  reaction  is 
reversible  : 

As2O3  +  2  H2O  +  2  I2  -^  4  HI  +  As2O5. 

If  the  hydriodic  acid  is  removed  from  the  solution  as  fast  as  it  is 
formed,  the  arsenious  oxide  will  be  completely  oxidized  to  the 
arsenic  oxide.  The  function  of  the  sodium  bicarbonate,  therefore, 
is  to  remove  the  hydriodic  acid  as  rapidly  as  it  is  formed. 

c.    By  Means  of  Standard  Permanganate  Solution 

Principle.  —  Potassium  permanganate  reacts  with  an  acid  solu- 
tion of  potassium  iodide,  liberating  iodine  quantitatively  according 
to  the  equation  : 


The  iodine  may  be  titrated  by  means  of  standard  thiosulphate. 

Procedure.  —  Introduce  25  c.c.  of  the  standard  permanganate 
solution  into  an  Erlenmeyer  flask  which  contains  10  c.c.  of  dilute 
sulphuric  acid  and  one  or  two  grams  of  potassium  iodide.  Add 


82  QUANTITATIVE  ANALYSIS 

100  c.c.  of  water  and  titrate  the  liberated  iodine  with  thiosulphate 
solution  until  the  solution  has  changed  to  a  straw  color,  then  add 
about  2  c.c.  of  the  starch  solution.  Continue  the  titration  until 
the  solution  changes  from  blue  to  colorless.  From  the  available 
oxygen  in  25  c.c.  of  the  permanganate  solution  calculate  the  num- 
ber of  grams  of  iodine  liberated,  and  the  strength  of  the  iodine 
solution  in  grams  of  iodine  per  cubic  centimeter. 

d.    By  Means  of  Standard  Dichromate  Solution 

Principle. — The  method  is  based  upon  the  fact  that  a  solution 
of  potassium  dichromate  liberates  iodine  from  an  acid  solution  of 
potassium  iodide,  the  equation  being 

K2Cr2O7  +  6  KI  +  14  HC1  =  8  KC1  +  2  CrCl3  +  7  H2O  +  3  I2. 

The  iodine  liberated  is  titrated  with  sodium  thiosulphate  solution. 
Procedure.  —  Place  25  c.c.  of  the  standard  dichromate  solution 
into  a  500  c.c.  Erlenmeyer  flask  containing  5  or  6  c.c.  of  concen- 
trated hydrochloric  acid  and  about  two  grams  of  potassium  iodide 
dissolved  in  25  c.c.  of  water.  Mix  thoroughly.  Dilute  to  about 
250  c.c.  and  run  in  sodium  thiosulphate  solution  as  in  the  stand- 
ardization by  means  of  permanganate.  In  this  case  the  transition 
is  from  blue  to  a  pale  green.  From  the  data,  calculate  the  strength 
of  the  iodine  solution  in  terms  of  grams  of  iodine  per  cubic 
centimeter. 

EXERCISE   XXVIII 
Estimation  of  Available  Chlorine  in  Bleaching  Powder 

Procedure.  —  Weigh  about  10  grams  of  bleaching  powder  into  a 
porcelain  mortar,  pulverize  thoroughly  in  the  presence  of  a  little 
water  until  the  mixture  is  of  the  consistency  of  thick  cream.  Add 
more  water,  allow  to  settle,  and  decant  into  a  liter  flask.  Grind  the 
residue  with  a  little  water,  and  continue  the  process  until  the  last 
trace  has  been  introduced  into  the  flask  without  loss.  Make  up 
to  the  mark  and  shake  thoroughly.  From  the  well-mixed  milky 
solution  remove  25  c.c.  by  means  of  a  pipette  and  introduce  it  into 
an  Erlenmeyer  flask.  Dissolve  two  grams  of  potassium  iodide  in 
25  c.c.  of  water,  add  it  to  the  solution,  and  acidify  with  acetic  acid. 
Titrate  the  iodine  liberated  in  the  usual  manner  with  sodium  thio- 
sulphate. Repeat,  and  when  the  ratio  between  this  solution  and 


VOLUMETRIC  ANALYSIS       •  83 

the  sodium  thiosulphate  is  established,  calculate  the  percentage  of 
available  chlorine  in  the  sample. 

Notes.  —  i.  Commercial  bleaching  powder  is  usually  a  mixture 
of  calcium  hypochlorite,  calcium  chloride,  and  hydroxide.  The 
true  bleaching  agent  is  the  hypochlorite.  In  general,  it  is  valued 
and  sold  by  the  percentage  of  chlorine  available  for  oxidizing 
purposes. 

2.  Chlorates  are  sometimes  present  in  bleaching  powder,  owing 
to  faulty  manufacture.  In  the  presence  of  acetic  acid,  these 
chlorates  do  not  liberate  iodine. 

EXERCISE   XXIX  ' 
The  Determination  of  Available  Oxygen  in  Pyrolusite 

Principle.  —  When  manganese  dioxide  is  heated  with  hydro- 
chloric acid,  chlorine  is  liberated.  The  chlorine  may  be  con- 
ducted into  a  so- 
lution of  potas- 
sium iodide,  and 
the  liberated  io- 
dine  titrated 
with  thiosul- 
phate. 

Procedure.  - 
Set  up  an  appa- 
ratus similar  to 
that  shown  in 
Fig.  20.  Use  a 
75  c.c.  glass- 
stoppered  retort 
and  a  250  c.c.  FlG'  20 

flask  which  should  be  so  arranged  that  a  stream  of  cold  water 
flows  upon  it.  Introduce  into  the  flask  about  10  grams  of  potas- 
sium iodide  dissolved  in  150  c.c.  of  water,  which  should  entirely 
cover  the  end  of  the  retort  when  it  is  in  place.  Weigh  into  the 
retort  0.5  gram  of  finely  pulverized  pyrolusite  and  add  30  c.c.  of 
concentrated  hydrochloric  acid.  Add  two  or  three  pieces  of  mag- 
nesite  the  size  of  a  pea  and  place  the  stopper  in  the  retort.  Heat 
the  contents  of  the  retort  to  boiling,  using  a  small  flame,  and  distill 


84  QUANTITATIVE  ANALYSIS 

about  one-half  of  the  liquid  over  into  the  flask.  In  order  to  pre- 
vent the  iodine  solution  from  being  drawn  back  into  the  retort, 
withdraw  the  delivery  tube  from  the  potassium  iodide  solution 
before  removing  the  flame.  Wash  off  the  end  of  the  delivery  tube. 
Transfer  the  contents  of  the  flask  to  a  250  c.c.  graduated  flask, 
make  up  to  the  mark,  mix  thoroughly,  and  titrate  50  c.c.  portions 
with  the  thiosulphate  solution  until  concordant  results  are  obtained. 
From  the  data  calculate  the  percentage  purity  of  the  pyr6lusite 
and  the  available  oxygen  in  one  gram. 

Notes.  —  i.  The  available  oxygen  in  chromates,  lead  peroxide, 
red  lead,  and  certain  other  oxidizing  substances  may  also  be  esti- 
mated in  this  way. 

2.  The  magnesite  dissolves  slowly  in  the  hydrochloric  acid,  and 
the  carbon  diqxide  liberated  prevents  the  liquid  from  drawing  back. 

3.  The  receiving  flask  should  be  cooled  to  prevent  the  loss  of 
iodine  by  volatilization. 

4.  The  apparatus  designed  by  Bunsen  can  also  be  employed  for 
such  determinations. 

EXERCISE   XXX 
Determination  of  the  Strength  of  Hydrogen  Peroxide 

Procedure.  —  Dilute  10  c.c.  of  the  hydrogen  peroxide  solution  to 
250  c.c.,  mix  thoroughly.  Introduce  25  c.c.  of  this  solution  into 
an  Erlenmeyer  flask  in  which  one  gram  of  potassium  iodide  dis- 
solved in  a  little  water  and  30  c.c.  of  dilute  sulphuric  acid  have 
been  placed.  After  five  minutes  dilute  to  100  c.c.  and  titrate  with 
the  standard  thiosulphate  in  the  usual  manner.  Repeat,  and  from 
the  data  calculate  the  percentage  of  hydrogen  peroxide  in  the 
sample,  assuming  the  specific  gravity  to  be  one.  Calculate  the 
number  of  grams  of  available  oxygen  in  each  cubic  centimeter  of 
the  original  peroxide  solution. 

Note.  —  The  stated  order  of  adding  the  reagents  must  be  followed, 
as  potassium  iodide  when  added  to  a  neutral  solution  of  hydrogen 
peroxide  decomposes  it  catalytically,  with  the  evolution  of  oxygen. 


PART    IV 

AGRICULTURAL   ANALYSIS    ; 

THE   ANALYSIS   OF   MILK 

MILK  is  the  natural  secretion  of  the  mammary  glands  of  female 
mammals  for  the  nourishment  of  their  young.  The  milk  of  the 
cow  is  of  most  importance  and  has  been  studied  in  greatest 
detail. 

Whole  Milk  is  the  lacteal  secretion  obtained  by  the  complete 
milking  of  one  or  more  healthy  cows,  properly  fed  and  kept,  ex- 
cluding that  obtained  within  fifteen  days  before  and  five  days  after 
calving. 

Standard  Milk  is  milk  containing  not  less  than  12  per  cent  of 
total  solids  and  not  less  than  8j  per  cent  of  solids  not  fat,  nor  less 
than  3^  per  cent  of  milk  fat. 

Fresh  cow's  milk  is  amphoteric,  that  is,  if  tested  with  blue  litmus 
paper  it  reacts  acid,  while  with  red  litmus  it  reacts  alkaline.  On 
standing  it  becomes  distinctly  acid,  and  the  acidity  increases  as  the 
milk  sugar  is  changed  by  bacterial  action  into  lactic  acid. 

COMPOSITION 

The  constituents  of  milk  are  water,  fat,  proteids,  milk  sugar 
(lactose),  and  inorganic  salts.  The  lactose,  albumin,,  and  certain 
salts  are  present  in  solution.  The  casein  does1  not  form  a  true 
solution,  but  is  present  in  a  colloidal  form  in  combination  with 
calcium  phosphate.  The  fat  is  present  in  minute  globules  which 
are  suspended  in  the  liquid.  Milk  from  other  animals  contains 
the  same  constituents  as  cow's  milk,  but  in  different. proportions. 
The  following  table,  compiled  by  Konig,  gives  the  composition  of 
some  of  the  different  kinds  of  milk  : 

85 


86 


QUANTITATIVE  ANALYSIS 


No.  OF 
ANALYSES 

SP.  GR. 

WATER 

CA- 
SEIN 

ALBU- 
MIN 

TOTAL 
PRO 

TEIDS 

FAT 

MILK 

SUGAR 

ASH 

Cow's  Milk  .     . 

800 

Minimum      .     . 

1  .0264 

89.32 

1.79 

0.25 

2.07 

1.67 

2.  II 

0-35 

Maximum      .     . 

1.0370 

90.69 

6.29 

1.44 

6.40 

647 

6.12 

1.  21 

Mean  .... 

1.0315 

87.17 

3.02 

o-53 

3-55 

3-64 

4-88 

0.71 

Human  Milk    .     . 

200 

Mean  .... 

1.029 

87.41 

1.03 

1.26 

2.29 

378 

6.21, 

0.31 

Goat's  Milk      .     . 

200 

Mean  .     . 

1.0305 

85.71 

3.20 

1.09 

4.29 

4.78 

4.46 

0.76 

SAMPLING 

To  insure  a  representative  sample,  the  milk  should  be  thoroughly 
mixed  by  pouring  from  one  vessel  to  another.  Where  this  is  im- 
possible, a  Scovell  sampling  tube,  which  permits  samples  to  be 
removed  from  any  part  of  the  container,  may  be  used.  The 
samples  taken  in  this  way  are  mixed  and  used  for  the  analysis. 

It  will  be  found  best  to  prepare  apparatus  so  that  the  various 
determinations  can  all  be  started  at  once.  The  following  appa- 
ratus will  be  necessary  in  addition  to  that  supplied  for  the  ordinary 
quantitative  work  : 

2  aluminium  dishes,  -2-f"  diameter. 
2  strips  of  fat-free  paper. 
2  Babcock  test  bottles, 
i  pipette,  17.6  c.c. 
i  cylinder,  17.5  c.c. 

Clean  the  aluminium  dishes  and  two  Erlenmeyer  flasks  (125  c.c.) 
and  heat  them  at  ioo°-iio°  in  the  air  bath  until  the  weight  is 
constant.  Heat  two  porcelain  dishes  over  the  flame  of  a  Bunsen 
burner,  cool,  and  weigh.  Repeat  until  the  weight  is  constant. 
Thoroughly  clean  two  Kjeldahl  flasks,  a  500  c.c.  graduated  flask, 
and  the  two  Babcock  test  bottles. 

Specific  Gravity 

Obtain  a  sample  of  milk,  a  thermometer,  a  hydrometer,  and  a 
250  c.c.  graduated  cylinder.  Thoroughly  mix  the  milk  by  pouring 
it  from  the  cylinder  into  a  beaker  and  back  again,  three  or  four 


AGRICULTURAL  ANALYSIS  87 

times.  Now  cover  the  cylinder  with  a  small  beaker,  place  it 
under  the  tap,  and  allow  water  to  run  upon  the  side  until  the  milk 
is  cooled  to  15.6°  C.,  at  which  temperature  determine  the  specific 
gravity  with  a  delicate  hydrometer  (lactometer). 

Notes.  —  i.  The  specific  gravity  of  milk  may  be  taken  by  means 
of  an  ordinary  hydrometer.  Hydrometers  for  use  with  milk  are 
known  as  lactometers  and  are  graduated  variously.  The  following 
lactometers  are  in  general  use  : 

The  Quevenne  lactometer  is  graduated  from  15°  to  40°,  and 
corresponds  to  specific  gravities  from  1.015  to  1-040. 

The  New  York  Board  of  Health  lactometer  has  an  arbitrary 
scale,  divided  into  120  equal  parts,  the  zero  being  equal  to  the 
specific  gravity  of  water,  while  100  corresponds  to  a  specific  gravity 
of  1.029. 

2.  The  specific  gravity  of  milk  depends  upon  two  factors,  the 
percentage  of  fat  present,  and  the  percentage  of  solids  other  than 
fat.     The  removal  of  fat  raises  the  specific  gravity ;  and  as  the 
specific  gravity  may  be  brought  back  by  the  addition  of  water,  it 
will   be    seen  that,  considered  by  itself,  specific  gravity  gives  no 
indication  of  the  purity  of  milk. 

3.  The  temperature,  1 5.6°  C.  (60°  F.),  is  the  standard  temperature 
for  taking  the  specific  gravity  of  milk.     Instead  of  cooling  the 
milk  to  this  temperature,  the  Specific  gravity  may  be  taken  at  the 
ordinary  temperature,  and  by  means  of    tables  calculated  to  the 
temperature  15.6°.     (See  Vieth's  tables  in  Leach's  Food  Analysis, 

P-  97-) 

Removal  of  Samples 

While  the  milk  is  at  the  temperature  at  which  the  specific  gravity 
was  determined,  remove  all  of  the  samples  required  for  analysis  as 
soon  as  possible,  and  proceed  with  the  respective  analyses  as 
described  below. 

Total  Solids 

Procedure.  —  Place  into  each  of  the  weighed  aluminium  dishes 
5  c.c.  of  milk,  evaporate  to  dryness  on  a  water  bath,  and  dry  in  the 
water  oven  for  exactly  one  hour,  at  the  temperature  of  boiling 
water.  Cool  in  the  desiccator,  and  weigh  rapidly  to  avoid  the 
absorption  of  hygroscopic  moisture.  Heat  in  the  water  oven  again 


88  QUANTITATIVE  ANALYSIS 

for  exactly  thirty  minutes,  cool,  and  weigh.     Calculate  the  percent- 
age of  total  solids  in  the  sample. 

Note.  —  The  total  solids  consist  of  sugar,  fat,  proteids,  and  inor- 
ganic salts.  As  certain  of  the  milk  constituents  undergo  decompo- 
sition when  heated  above  100°,  the  water  oven  and  not  the  air  bath 
should  be  used  for  drying  the  solids.  A  darkening  of  the  solid 
matter  indicates  decomposition. 

Ash 

Procedure.  —  Place  25  c.c.  of  milk  into  each  of  the  weighed  por- 
celain dishes,  add  5  c.c.  of  concentrated  nitric  acid,  evaporate  to 
dryness  on  the  water  bath,  and  then  burn  at  a  low  red  heat  in  the 
muffle  furnace  (see  Fig.  21)  until  the  ash  is  free  from  carbon. 
Heat  to  constant  weight  and  calculate  the  percentage  of  ash. 

Notes.  —  i.  The  ash  from  a  large  number  of  samples  on  analy- 
sis gave  the  following  composition : 

Potassium  oxide      .     .     .     .     .     .     .  25.02% 

Sodium  oxide     .....     .     .     .  10.01 

Calcium  oxide    .     .     .     .  , 20.01 

Magnesium  oxide  .     .     .  -*.     .     .     .  2.42 

Iron  oxide     .     .     .     ....     .     .  0.13 

Sulphur  trioxide     .     .     ,     ,.     .     ...  3.84 

Phosphorus  pentoxide 24.29 

Chlorine   .     .     .     .....     .     .  14.28 

100.00 

2.  The  ash  should  not  be  heated  higher  than  a  dull  red  heat,  as 
there  is  considerable  danger  of  volatilizing  the  sodium  and  potas- 
sium chlorides  which  form  a  large  percentage  of  the  inorganic 
constituents  of  milk. 

Fat 

Adams'  Paper  Coil  Method 

Procedure.  —  Suspend  strips  of  fat-free  paper  from  the  edge  of 
the  desk  and  deliver  evenly  upon  each  exactly  5  c.c.  of  milk  from 
a  pipette.  Allow  the  paper  to  dry  partially,  then  roll  into  a  coil, 
bind  with  a  clean  tinned  iron  wire,  place  both  coils  into  a  small 
beaker,  and  dry  in  the  water  oven  at  100°  C.  for  two  hours.  Place 
the  coils  into  large  inner  extraction  tubes  over  the  ends  of  which 


FIG.  21 


QUANTITATIVE  ANALYSIS 


V 


v 


FIG.  22 


pieces  of  hard  fat-free  filter  paper 
have  been  fastened  by  means  of 
tinned  iron  wire  (see  Fig.  22,  A). 
Place  the  inner  extraction  tubes 
inside  two  Soxhlet  extractors, 
attach  to  the  Hopkins  conden- 
sers, connect  with  clean  weighed 
Erlenmeyer  flasks  into  which  50 
c.c.  of  dry  ether  have  been  placed, 
and  extract  for  two  hours.  The 
arrangement  of  the  apparatus  is 
shown  in  Fig.  22.  The  Erlen- 
meyer flask  is  best  heated  by 
means  of  an  electric  air  bath  as 
illustrated  in  Fig.  23.  Connect 
the  flasks  containing  the  ether 
with  condensers  which  are  set  up 
for  this  purpose,  and  recover  the 
ether  by  distillation.  The  distil- 
lation apparatus  is  shown  in  Fig. 
24.  Dry  the  flask  and  fat  in  the 
water  oven  to  constant  weight 
and  calculate  the  percentage  of 
fat  in  the  milk. 

Babcock  Method 

Procedure.  —  Measure  out  17.6 
c.c.  of  milk  with  a  Babcock  pi- 
pette, transfer  to  a  Babcock  test 
bottle,  and  add  in  small  portions 
17.5  c.c.  of  commercial  sulphuric 
acid,  shaking  the  flask  after  each 
addition.  .  Thoroughly  mix  the 
acid  and  the  milk,  until  the  curd 
which  separates  at  first  is  com- 
pletely dissolved.  Prepare  dupli- 
cates at  the  same  time.  Imme- 
diately place  the  bottles  into  the 
centrifugal  machine  (Fig.  25) 


AGRICULTURAL  ANALYSIS  91 

opposite  each  other,  replace  the  cover,  and  turn  the  machine  at  a 
high  speed  for  five  minutes.  Now  fill  the  bottles  with  very  hot 
distilled  water  to  about  the  7  per  cent  mark.  Turn  the  machine 


FIG.  23 

for  one  minute  more,  remove  the  bottle,  and  immediately,  while 
still  hot,  determine  the  percentage  of  fat  by  measuring  the  length 
of  the  fat  column  with  a  pair  of  dividers.  The  graduation  of  the 
neck  of  the  flask  reads  percentage  of  fat  direct.  The  test  bottles 
are  so  made  that  the  length  of  the  fat  column  is  read  from  the 


92  QUANTITATIVE  ANALYSIS 

bottom  of  the  lower  meniscus,  which  should  be  nearly  flat,  to  the 
point  at  which  the  upper  meniscus  meets  the  side  of  the  neck. 

Notes.  —  I.  Milk  fat  is  a  mixture  of  glycerides  of  which  palmi- 
tin,  olein,  myristin,  and  butyrin  are  the  most  important.  The  de- 
termination of  fat  by  the  Adams  method  is  based  upon  the  fact 


FIG.  24 


that  it  is  soluble  in  ether,  while  the  other  solids  are  insoluble.  The 
fat  must  be  thoroughly  dried  before  it  can  be  extracted ;  this  is 
best  accomplished  by  distributing  it  upon  a  strip  of  fat-free  paper, 
allowing  most  of  the  water  to  evaporate  in  the  air,  and  removing 
the  last  portion  by  heating  in  the  water  oven.  The  greater  part 
of  the  fat  is  left  on  the  surface  of  the  paper,  so  that  it  is  easily 
extracted  with  ether.  On  heating  the  flasks  to  constant  weight, 
care  should  be  taken  that  the  fat  is  not  heated  too  long  nor  at  too 
high  a  temperature,  inasmuch  as  on  one  hand  volatile  fatty  acids 
may  escape,  causing  a  loss,  while  on  the  other  hand  an  increase  in 
weight  may  take  place  due  to  oxidation. 

2.    In  the  determination  of  fat  by  the  Babcock  method,   sul- 


AGRICULTURAL  ANALYSIS 


93 


phuric  acid  dissolves  the  casein  and  sets  the  fat  free  in  a  pure  state. 
By  rotating  in  the  centrifugal  the  fat  is  collected  in  the  neck  of  the 
flask.  Since  the  volume  of  fat  contracts  on  cooling,  the  reading 
should  be  taken  while  it  is  liquid.  The  color  of  the  fat  should  be 
yellow.  If  the  acid  used  is  too  dilute,  white  particles  of  casein  will 
be  mixed  with  the  fat ;  if  too  concentrated,  the  fat  will  contain 


FIG.  25 

charred  matter  due  to  the  action  of  concentrated  acid  on  the  or- 
ganic matter  present  in  the  milk.  The  sulphuric  acid  used  should 
have  a  specific  gravity  between  1.82  and  1.83  at  15.0°  C. 

3.  Based  on  the  close  relationship  between  the  fat,  the  specific 
gravity,  and  the  solids  not  fat,  formulas  have  been  derived  by 
which,  if  two  of  these  factors  are  known,  the  third  may  be  calcu- 
lated. The  formula  in  common  use  in  this  country  is  that  pro- 
posed by  Babcock.1 


Solids  not  fat  = 


i  oo  S  —  FS 


i    (loo-  F)  2.5. 


.100  -  1,0753/0 
is  the  specific  gravity  and  F  the  percentage  of  fat. 

1  U.  S.  Dept.  of  Agric.,  Div.  of  Chem.,  Bui.  47,  p.  123. 


94  QUANTITATIVE  ANALYSIS 

Total  Proteids 
Determination  of  Total  Nitrogen  by  the  Kjeldahl  Method 

Principle. — The  determination  of  the  proteids  is  based  upon 
the  fact  that  about  16  per  cent  of  proteid  matter  is  nitrogen. 
The  nitrogen  in  the  proteids  can  be  changed  completely  to  ammo- 
nium sulphate  by  digestion  with  concentrated  sulphuric  acid,  and 
the  ammonia  in  this  compound  distilled  into  standard  acid  and 
determined  volumetrically.  From  the  amount  of  ammonia,  the 
nitrogen,  and  consequently  the  amount  of  proteid  matter,  can  be 
calculated. 

Procedure.  —  Measure  carefully  5  c.c.  of  milk  into  a  500  c.c. 
Kjeldahl  digestion  flask,  taking  care  that  the  milk  does  not  get 
upon  the  neck  of  the  flask.  Add  25  c.c.  of  pure  concentrated 
sulphuric  acid  and  about  0.65  gram  of  metallic  mercury.  Take 
into  the  digestion  room,  incline  the  flask  on  a  stand  (see  Fig.  26) 
at  an  angle  of  30°,  and  commence  heating,  watching  closely  at 
first,  as  there  is  danger  of  foaming  during  the  first  five  to  ten 
minutes ;  after  that  the  acid  may  be  brought  to  boiling.1  Con- 
tinue the  digestion  for  two  hours,  or  until  the  liquid  is  colorless, 
keeping  the  acid  boiling  briskly  all  the  time.  See  that  all  charred 
particles  are  washed  down  by  the  acid.  After  heating  for  two 
hours,  if  the  solution  is  not  clear,  finish  the  oxidation  by  the 
careful  addition  of  a  little  powdered  potassium  permanganate  and 
allow  the  contents  of  the  flasks  to  cool. 

During  the  digestion  obtain  the  condenser,  stands,  and  other 
parts  of  the  distilling  apparatus,  and  arrange  them  as  represented 
in  Fig.  27.  Place  about  200  c.c.  of  nitrogen-free  water  into  each 
of  two  other  Kjeldahl  flasks,  attach  to  the  condensers  and  distill 
over  without  condensing  the  steam,  thus  cleaning  out  the  condens- 
ers thoroughly.  Allow  the  contents  of  the  flasks  in  which  the 
digestion  took  place  to  cool,  add  200  c.c.  of  nitrogen-free  water 
and  25  c.c.  of  potassium  sulphide  solution,  shaking  thoroughly 
after  the  addition  of  the  latter  solution.  Add  three  or  four  small 

1  A  convenient  form  of  digestion  apparatus  was  devised  at  the  Connecticut  Experi- 
ment Station  and  is  shown  in  Fig.  26.  To  avoid  the  fumes  from  digestion,  the  necks  of 
the  flasks  are  inserted  into  a  lead  pipe  through  openings  in  the  side.  The  lead  pipe  is 
connected  with  a  flue  having  a  good  draft.  A  detailed  description  of  this  apparatus  can 
be  found  in  the  Twenty-first  Annual  Report  of  the  Agricultural  Experiment  Station, 
University  of  Wisconsin,  pages  361-362  (1904). 


96 


QUANTITATIVE  ANALYSIS 


pieces  of  granulated  zinc.  Measure  carefully  into  250  c.c.  Erlen- 
meyer  flasks  30  c.c.  of  standard  sulphuric  acid,  label  the  flasks 
properly,  and  add  to  each  a  few  drops  of  methyl  orange  indicator. 
Connect  the  flasks  containing  the  standard  acid  with  the  con- 


FIG.  27 

densers.  Then  incline  the  digestion  flask  and  pour  70-80  c.c.  of 
sodium  hydroxide  solution  (600  grams  per  liter)  down  the  side  of 
the  neck,  being  careful  not  to  mix  the  alkali  with  the  acid  con- 
tents. Wash  the  neck  of  the  flask  free  from  alkali  with  a  little 
nitrogen-free  water,  and  connect  it  immediately  with  the  proper 
condenser.  Be  sure  that  the  tips  of  the  delivery  tubes  are 


AGRICULTURAL  ANALYSIS  97 

immersed  in  the  standard  acid  and  that  the  water  is  running 
through  the  condenser ;  then  mix  the  contents  of  the  digestion 
flask  thoroughly.  Heat  very  carefully  at  first  and  distill  over 
175-200  c.c.  of  the  liquid,  taking  about  an  hour  for  the  distillation. 
Watch  the  solution  throughout  the  distillation,  as  there  is  danger 
of  foaming  and  bumping.  Disconnect  the  flasks  before  removing 
the  burners  and  wash  off  the  delivery  tubes  into  the  Erlenmeyer 
flasks  with  distilled  water. 

Titrate  the  excess  of  acid  in  the  receiving  flasks  with  a  solution 
of  standard  ammonium  hydroxide.  (This  should  be  standardized 
by  titrating  against  the  same  standard  sulphuric  acid  that  was  used 
in  the  receiving  flasks.)  From  the  data  calculate  the  number  of 
cubic  centimeters  of  the  standard  acid  which  have  been  neutralized 
by  the  ammonia  distilled  over.  Subtract  from  this  the  number  of 
cubic  centimeters  of  the  standard  sulphuric  acid  solution  neutral- 
ized by  the  ammonia  from  the  blank  determination  described 
below.  The  difference  gives  the  number  of  cubic  centimeters  of 
the  standard  acid  neutralized  by  the  ammonia  formed  from  the 
milk  proteids.  From  this  value  and  the  strength  of  the  standard 
acid  (see  factor  on  the  bottle)  calculate  the  amount  of  nitrogen 
formed  from  the  milk  proteids,  and  then  calculate  the  percentage 
of  nitrogen  in  the  sample.  The  percentage  of  nitrogen  multiplied 
by  the  factor  6.25  gives  the  percentage  of  proteids.  For  the 
method  of  calculation  see  page  175. 

Determination  of  the  Blank 

The  reagents  used  in  the  Kjeldahl  process  almost  always  contain 
small  amounts  of  nitrogenous  compounds.  This  is  particularly 
true  of  sulphuric  acid.  It  is  always  necessary,  therefore,  to  make 
a  "  blank  "  to  correct  for  the  nitrogenous  constituents  in  the  re- 
agents. This  is  done  by  adding  the  usual  amount  of  sulphuric 
acid  to  one  gram  of  sugar,  and  digesting  in  a  Kjeldahl  flask  with 
mercury,  carrying  out  the  rest  of  the  determination  as  in  the  deter- 
mination of  the  milk  proteids.  The  correction  found  by  the  blank 
is  conveniently  expressed  in  terms  of  the  number  of  cubic  centi- 
meters of  the  standard  acid  necessary  to  neutralize  the  ammonia 
present  in  the  reagents. 

Notes. —  i.  The  total  proteids  in  milk  have  the  following  com- 
position : 


98  QUANTITATIVE  ANALYSIS 

Casein 80% 

Lactalbumin 15 

Traces  of  other  nitrogenous  substances    5 

Casein  is  a  white  odorless  and  tasteless  substance  which  is 
sparingly  soluble  in  water,  readily  soluble  in  dilute  alkalies,  and 
insoluble  in  alcohol  and  ether.  Strong  acids  dissolve  it,  but  its 
nature  is  changed. 

2.  Sulphuric  acid  at  a  high  temperature  acts  as  an   oxidizing 
agent,  oxidizing  the  organic  compounds  present  in  milk  to  carbon 
dioxide  and  water.     The  nitrogen  present  forms  ammonium  sul- 
phate.    The  mercury  is  dissolved,  forming  mercuric  sulphate,  its 
function  being  to  make  oxidation  take  place  more  rapidly.     A  sub- 
stance acting  in  this  way  is  called  a  "catalyzer."     Mercury  salts 
form  complex  compounds  with  ammonium  salts  from  which  the 
ammonia  may  be  liberated  only  with  difficulty.     It  is  necessary, 
therefore,  to  break  up  these  complexes.     This  can  be  done  by  the 
addition  of  potassium  sulphide. 

3.  If  the  sodium  hydroxide  solution  is  mixed  at  once  with  the 
contents  of  the  Kjeldahl  flask,  the  solution  will  become  so  hot  that 
there  will  be  danger  of  loss  of  ammonia  by  volatilization.     Great 
care  should  be  exercised  at  this  point,  and  the  flask  should  be  con- 
nected with  the  condenser  as  soon  after  the  addition  of  the  alkali 
as  possible.     As  there  is  danger  of  "  bumping  "  when  the  flasks  are 
heated,  a  few  pieces  of  granulated  zinc  are  usually  added  just  before 
the  addition  of  the  alkali,  which  prevent  bumping  by  dissolving  in 
the  alkali  with  the  liberation  of  hydrogen,  which  keeps  the  solution 
stirred.     Fragments   of   ignited   pumice   stone  will   also   prevent 
bumping. 

4.  In  the  determination  of  the  blank,  the  function  of  the  sugar 
is  to  reduce  any  nitrates  which  might  be  present  in  the  reagents. 

5.  The  Kjeldahl  method  for  the  determination  of  nitrogen  finds 
wide  application  in  the  analysis  of  agricultural  products.     For  the 
determination  of  nitrogen  in  nitrates,  the  method  cannot  be  used  in 
the  form  described.     For  this  purpose  a  modification  of  the  process 
is  used,  in  which  the  nitrates  are  first  reduced  to  ammonium  com- 
pounds. 

6.  Potassium  sulphate  is  often  added  to  the  digestion  flask  with 
the  sulphuric  acid,  in  the  presence  of  which  it  forms  potassium  acid 
sulphate.     This  raises  the  boiling  point  of  the  solution  and  makes 
the  oxidation  take  place  more  rapidly. 


AGRICULTURAL  ANALYSIS  99 

7.  The  term  "  protein  "   is  often  used  to  designate  the  results 
obtained  by  multiplying  the  total  nitrogen  by  the  factor  6.25. 


Milk  Sugar  by  Soxhlet's  Method 

Principle. — The  determination  of  lactose  depends  upon  the  fact 
that  in  an  alkaline  solution  certain  sugars,  among  which  are  lactose, 
dextrose,  and  levulose,  together  with  some  other  organic  compounds, 
have  the  power  of  reducing  the  copper  in  copper  tartrate  to  the 
cuprous  state,  cuprous  oxide  being  precipitated.  The  amount  of 
cuprous  oxide  formed  depends  upon  the  nature  of  the  reducing 
agent,  the  concentrations  of  the  substances  in  solution,  the  tem- 
perature of  the  solution,  and  on  the  length  of  time  the  solution  is 
heated. 

In  the  determination  of  lactose  certain  standard  conditions  have 
been  adopted  in  which  the  concentrations  of  the  reagents,  the  tem- 
perature, and  the  length  of  time  the  solution  is  heated  are  the  same 
in  every  determination.  A  definite  amount  of  cuprous  oxide, 
therefore,  always  corresponds  to  a  definite  amount  of  milk  sugar, 
and  a  table  has  been  prepared,  which  gives  for  any  amount  of 
cuprous  oxide,  obtained  under  these  conditions,  the  equivalent 
amount  of  lactose. 

Procedure.  —  Place  25  c.c.  of  milk  into  the  500  c.c.  measuring 
flask,  add  400  c.c.  of  water,  mix,  then  add  10  c.c.  of  the  Fehling's 
copper  sulphate  solution  and  8.8  c.c.  of  N/2  potassium  hydroxide 
solution.  Fill  the  flask  to  the  mark,  thoroughly  mix,  allow  the 
precipitate  to  settle,  and  filter  through  a  dry  ribbed  filter,  discarding 
the  first  10  c.c.  of  the  filtrate.  The  filtrate  should  have  an  acid 
reaction  and  contain  copper  in  solution.  In  the  solution  thus  pre- 
pared determine  the  milk  sugar  as  follows:  Place  25  c.c.  of  the 
standard  copper  sulphate  solution  and  25  c.c.  of  the  alkaline  tartrate 
solution  into  a  250  c.c.  casserole  and  heat  to  boiling.  While  boil- 
ing briskly,  add  100  c.c.  of  the  milk  solution  and  boil  vigorously 
for  six  minutes.  Filter  immediately  without  diluting,  through  a 
quantitative  filter  paper.  Be  sure  that  the  filtrate  is  perfectly  clear ; 
if  not,  refilter.  Wash  immediately  with  boiling  distilled  water  until 
the  wash  water  no  longer  reacts  alkaline.  Transfer  filter  and  con- 
tents to  a  weighed  crucible  and  dry  carefully.  When  dry,  ignite 
the  precipitate  at  red  heat  for  about  20  minutes.  Transfer  quickly 
to  the  desiccator,  cool,  and  weigh.  Ignite  to  constant  weight.  As 


100  QUANTITATIVE  ANALYSIS 

cupric  oxide  is  somewhat  hygroscopic,  weigh  as  quickly  as  possible. 
From  the  weight  of  the  cupric  oxide  obtained,  calculate  the  amount 
of  copper.  Obtain  the  weight  of  milk  sugar  equivalent  to  the 
weight  of  copper  from  Table  VI  on  page  206.  Calculate  the 
percentage  of  lactose  in  the  sample. 

Notes.  —  i .  Since  the  casein  in  th  e  milk  reduces  the  alkaline  copper 
tartrate  to  a  certain  extent  it  must  be  removed.  This  is  done  by 
precipitating  copper  hydroxide  in  the  solution,  the  precipitate  car- 
rying down  with  it  all  the  casein,  which  is  then  removed  by  filtration. 

2.  The  alkaline  solution  of  copper  tartrate  is  known  as  "  Feh- 
ling's  solution."  It  is  usually  prepared  at  the  time  of  using  by 
mixing  a  solution  of  copper  sulphate  and  a  solution  of  sodium 
potassium  tartrate  containing  sodium  hydroxide.  If  kept  mixed 
for  any  length  of  time,  Fehling's  solution  undergoes  a  change,  so 
that  on  boiling  cuprous  oxide  is  precipitated  even  when  no  lactose 
is  present. 

Tabulation  of  the  Results 

Collect  the  results  obtained  in  this  analysis  and  neatly  tabulate 
them  on  one  page  of  the  laboratory  notebook. 


REFERENCES 

FARRINGTON  AND  WOLL,  Testing  Milk  and  its  Products  (1904). 

RICHMOND,  Dairy  Chemistry  (1899). 

LEACH,  Food  Inspection  and  Analysis,  Chap.  VI,  p.  88  (1904). 


THE   ANALYSIS   OF  BUTTER 

Butter  is  the  clean  non-rancid  product  made  by  gathering  in  any 
manner  the  fat  of  fresh  or  ripened  milk  or  cream  into  a  mass,  which 
also  contains  a  small  portion  of  the  other  milk  constituents,  with  or 
without  salt,  and  contains  not  less  than  82.5  per  cent  of  milk  fat. 
By  acts  of  Congress  approved  August  2,  1886,  and  May  9,  1902, 
butter  may  also  contain  added  coloring  matter.1 

The  following  results  of  a  large  number  of  butter  analyses  by 
Konig  show  that  the  composition  may  vary  within  wide  limits. 

1  U.S.  Dept.  of  Agric.,  Office  of  the  Secretary,  Circular  No.  19  (1906). 


AGRICULTURAL  ANALYSIS 


101 


WATER 

FAT 

CASEIN 

LACTOSE 

LACTIC 
ACID 

SALTS 

Minimum    . 

4.15 

69.96 

0,19 

0-45 

0.00 

O.O2 

Maximum    . 

35-!5 

86.15 

4.78 

1.16 

1.16 

15.08 

Mean       .     .     . 

13-59 

84.39 

0.74 

0.12 

O.I2 

0.66  * 

On  exposure  to  light  and  air  butter  fat  acquires  a  disagreeable 
smell  and  taste ;  it  is  said  to  become  rancid.  The  quantity  of  free 
fatty  acids  is  greatly  increased  ;  the  volatile  acids  are  liberated  and 
their  odor  can  be  detected  in  the  rancid  butter.  Certain  oxidation 
products  are  also  formed.  In  regard  to  the  changes  which  take 
place  during  this  process,  but  little  is  known.  During  the  last 
few  years  processes  have  been  perfected  by  which  rancid  butter  is 
melted  and  treated  in  such  a  way  as  to  remove  the  objectionable 
odors  and  give  the  product  the  appearance  of  pure  butter.  This 
product  is  known  as  "  process/'  or  "  renovated,"  butter,  and  is  at 
present  manufactured  on  a  large  scale.  Standard  renovated  butter 
contains  not  more  than  16  per  cent  of  water  and  at  least  82.5  per 
cent  of  milk  fat. 

SAMPLING 

Place  from  200  to  300  grams  of  the  sample  to  be  analyzed  into 
a  glass-stoppered,  salt-mouthed  bottle  and  melt  the  butter  at  as 
low  a  temperature  as  possible.  When  melted  place  the  bottle 
into  ice  water  or  under  a  stream  of  cold  tap  water  and  shake  vio- 
lently until  the  mass  is  homogeneous  and  sufficiently  solidified  to 
prevent  the  separation  of  the  water  and  salt.  Nearly  fill  a  glass- 
stoppered  weighing  tube  with  the  butter  and  keep  in  a  cold  place 
until  analyzed. 

The  Determination  of  Water 

Procedure.  — Dry  from  1.5  to  2.5  grams  of  the  sample  to  constant 
weight  at  the  temperature  of  boiling  water  in  a  weighed,  flat-bottomed 
dish,  or  beaker,  which  has  a  surface  of  at  least  20  square  centime- 
ters. From  the  loss  of  weight  calculate  the  percentage  of  water 
present.  If  a  round-bottomed  dish  is  used,  the  complete  expulsion 
of  the  water  will  be  accomplished  with  difficulty,  owing  to  the  depth 
of  the  layer  of  fat.  In  this  case  a  small  stirring  rod  about  2\  inches 
long  should  be  weighed  with  the  dish  and  the  butter  fat  stirred 
occasionally  during  the  heating. 

1  Many  of  the  samples  were  unsalted,  hence  the  low  mineral  content. 


102  QUANTITATIVE  ANALYSIS 

The  Determination  of  Fat 

Procedure.  —  Dissolve  the  dry  butter  left  from  the  determination 
of  water  in  absolute  ether,  and  with  the  aid  of  a  glass-stoppered 
wash  bottle  containing  ether  transfer  the  contents  of  the  dish  to  a 
prepared  and  weighed  Gooch  crucible.  Wash  with  ether  until  free 
from  fat  and  heat  the  crucible  and  contents  in  the  water  oven 
until  the  weight  is  constant.  Calculate  the  percentage  of  fat  from 
the  data  obtained. 

Note.  —  Place  the  ether  residues  into  a  bottle  provided  for  that 
purpose. 

The  Determination  of  Casein  and  Ash 

Procedure.  —  Cover  the  crucible  containing  the  residue  from  the 
fat  determination,  and  heat  in  the  ash  muffle,  gradually  raising 
the  temperature  to  just  below  redness.  Remove  the  cover  and 
continue  the  heating  until  the  contents  of  the  crucible  are  white. 
The  loss  in  weight  of  the  crucible  and  contents  represents 
casein,  while  the  residue  in  the  crucible  is  mineral  matter. 

Note.  —  If  lactose  is  present,  it  will  be  burned  and  calculated  as 
casein.  By  obtaining  an  aqueous  extract  of  a  separate  portion  of 
butter,  the  lactose  may  be  determined  by  means  of  Fehling's  solu- 
tion, and  the  proper  correction  made. 

The  Determination  of  Salt 

Principle.  —  When  a  silver  nitrate  solution  is  added  to  a  neutral 
solution  of  an  alkali  or  an  alkaline  earth  chloride,  silver  chloride  is 
formed.  If  a  small  amount  of  potassium  chromate  is  present,  a 
reddish  brown  precipitate  of  silver  chromate  will  be  formed,  which 
disappears  on  stirring,  owing  to  the  fact  that  it  is  decomposed  by 
the  alkali  chloride,  according  to  the  equation : 

Ag2Cr04  +  2  NaCl  =  2  AgCl  +  Na2CrO4. 

After  the  chlorine  is  all  precipitated,  however,  the  next  drop  of 
silver  nitrate  precipitates  silver  chromate,  which  colors  the  solution 
a  permanent  reddish  brown. 

Procedure.  —  Weigh  into  a  tared  beaker  about  ten  grams  of  the 
sample.  Place  the  butter  into  the  beaker  in  portions  of  about  one 
gram,  removing  them  from  different  parts  of  the  sample  by  means 


AGRICULTURAL  ANALYSIS  103 

of  a  spatula.  Add  about  25  c.c.  of  boiling  water  to  the  beaker,  and 
after  the  fat  has  melted  pour  the  liquid  into  a  separatory  funnel, 
and  rinse  the  beaker  with  several  portions  of  hot  water.  Shake  the 
funnel  and  allow  it  to  stand  until  the  fat  has  collected,  then  draw 
off  the  underlying  aqueous  solution  into  a  250  c.c.  graduated  flask. 
Add  about  20  c.c.  of  hot  water  to  the  funnel,  extract  again,  and  re- 
peat the  extraction  until  about  225  c.c.  have  been  collected  in  the 
graduated  flask.  Cool  the  contents  of  the  flask  to  room  temperature 
and  make  the  volume  up  to  250  c.c. 

Place  50  c.c.  of  the  salt  solution  into  a  casserole  and  add  one 
cubic  centimeter  of  potassium  chromate  solution.  Add  from  a 
burette  a  solution  of  N/2O  silver  nitrate  until  the  solution  changes 
from  yellow  to  brown.  The  end  point  may  be  observed  more  easily 
if  a  casserole  containing  50  c.c.  of  water  and  one  cubic  centimeter 
of  the  indicator  be  placed  beside  the  one  containing  the  salt  solu- 
tion and  the  colors  of  the  two  solutions  compared  during  the  titra- 
tion.  A  blank  experiment  should  be  made  to  determine  how  much 
of  the  silver  nitrate  solution  is  necessary  to  produce  the  brown 
color  with  the  indicator  when  no  chloride  is  present,  and  this  amount 
should  be  subtracted  from  that  used  in  the  analysis.  From  the 
results  of  the  titration  calculate  the  percentage  of  sodium  chloride 
in  the  butter. 

Note.  —  Instead  of  potassium  chromate,  sodium  arsenate  solution 
may  be  used  as  an  indicator,  as  recommended  by  Lunge.  This 
has  the  advantage  of  changing  the  solution  from  colorless  to  red- 
dish brown,  making  the  end  point  easier  to  detect. 

THE  EXAMINATION  OF  BUTTER  FAT 

The  foregoing  tests  with  butter  are  of  value  in  showing  whether 
or  not  the  butter  contains  an  excessive  amount  of  salt  and  water. 
They  give  no  idea,  however,  of  the  possibility  of  the  presence  of 
animal  fat  which  may  have  been  used  to  adulterate  the  butter.  For 
this  purpose  an  examination  of  butter  fat  must  be  made. 

Composition  of  Butter  Fat 

Butter  fat  is  a  complex  mixture  of  glycerides  which  are  present 
in  varying  amounts.  Its  separation  into  the  various  constituents 
presents  many  difficulties,  and  the  results  obtained  by  different  in- 


IO4 


QUANTITATIVE  ANALYSIS 


vestigators  show  wide  variations.     An  investigation  by  Browne1 
shows  these  glycerides  to  be  present  in  the  following  proportions : 


PER  CENT 
PRESENT 

FORMULA  OF  ACID  FROM  WHICH 
GLYCERIDE  is  FORMED 

Dioxystearin   . 

1.04 

Ci7H33(OH)2COdH 

Glycerides  of  non- 
volatile acids  in-  . 

Olein      .... 
Stearin  .... 

33-95 
1.91 

Ci7H33COOH 
Ci7H35COOH 

soluble  in  water 

Palmitin     .     .     . 

40.51 

Ci5H31COOH     , 

Myristin 

10.44 

C13H,7COOH 

Laurin    .... 

2-73 

CnH23COOH 

Glycerides  of  vola- 
tile acids  soluble 

Caprin   .... 
Caprylin      .     .     . 
Caproin       .     .     . 

o-34 
o-53 

2.32 

CflHwCOOH 

C7Hi5COOH 
CsHnCOOH 

Butyrin 

6.23 

C3H7COOH 

Olein,.  stearin,  and  palmitin  are  the  most  common  of  the  insoluble 
glycerides.  Butyrin  is  the  most  important  of  the  soluble  glycerides. 
In  the  subsequent  discussion  these  glycerides  will  be  used  as  types 
of  their  respective  classes. 

The  most  frequent  form  of  butter  adulteration  consists  in  replac- 
ing the  fat,  either  entirely  or  in  part,  by  certain  other  fats.  Butter 
which  has  been  adulterated  in  this  way  is  known  as  oleomargarine 
or  butterine.  The  principal  substance  used  in  the  manufacture  of 
oleomargarine  is  oleo  oil,  a  product  obtained  from  the  fat  of  beef 
cattle,  which  is  essentially  a  mixture  of  olein  and  palmitin.  The 
oleo  oil  is  usually  churned  with  neutral  lard,  milk,  and  a  small 
amount  of  butter.  Coloring  matter  is  often  added  at  this  stage. 
The  whole  mass  is  then  cooled,  the  fat  separated  from  the  liquid, 
salted,  worked,  and  treated  similarly  to  butter.  Oils  of  vegetable 
origin,  such  as  cotton  seed,  peanut,  and  sesame,  are  occasionally 
mixed  with  the  oleo  oil.  Blyth  gives  the  following  proximate 
analysis  of  commercial  oleomargarine  : 


Insoluble  non-volatile  acids. 


Soluble  and  volatile  acids. 


1  Browne,  Jour.  Am.  Chem.  Soc.,  21,  823  (1899). 


PER  CENT 

Water 

.       .       .       .       12.01 

PER  CENT 

Casein 
Salt 

....          0-74 
527 

Palmitin 
Stearin 

22.32  • 
46.94 

Fat 

82.O2    « 

Olein 

30.42 

Butyrin     1 

Caproin 

0.32 

Caprylin    I 

AGRICULTURAL  ANALYSIS  105 

There  are  certain  important  fundamental  differences  between 
butter  fat  and  the  fat  found  in  oleomargarine,  which  may  be  briefly 
stated  as  follows  :  — 

I.  Chemical  Differences 

1.  About  5  per  cent  of  the  fatty  acids  in  butter  fat  are  soluble 
in  water  and  volatile  with  steam.     In  oleomargarine  these  soluble 
volatile  fatty  acids  form  a  much  smaller  part  of  the  fat,  never 
more  than  one  per  cent. 

2.  From  the  above  it  follows  that  the  percentage  of  insoluble 
fatty  acids  in  butter  fat  will  be  several  per  cent  less   than  that 
found  in  the  fat  of  oleomargarine. 

3.  Butter  fat  in  general  contains  a  smaller  percentage  of  unsatu- 
rated  fatty  acids  than  oleomargarine. 

4.  In    the   saponification  of   equal   amounts  of   butter  fat  and 
oleomargarine  a  larger  quantity  of  the  alkali  is  required  for  the 
butter  fat. 

II.  Physical  Differences 

5.  The  index  of  refraction  of  butter  fat   is  always  appreciably 
lower  than  that  of  oleomargarine.     This  is  the  most  important  of 
the  physical  differences. 

6.  The  specific  gravity  of  butter  fat  at  37.8°  C.  is  always  above 
0.910,  that  of  oleomargarine  rarely  above  0.904. 

7.  The  melting  point  of  butter  fat  is  usually  somewhat  higher 
than  that  of  oleomargarine. 

It  is  on  these  differences  that  the  methods  for  the  identification 
of  these  fats  are  based.  It  is  obvious,  however,  that  if  a  large 
amount  of  butter  fat  is  mixed  with  the  oleomargarine,  the  values  of 
the  constants  will  approach  those  of  pure  butter. 

Preparation  of  Pure  Butter  Fat 

Melt  about  100  grams  of  the  butter  in  a  beaker  by  allowing  it  to 
stand  in  a  dry  warm  place  at  about  60°.  When  the  water  and 
curd  have  entirely  settled,  pour  off  the  clear  supernatant  fat  through 
a  dry  filter  paper  placed  in  a  jacketed  funnel  containing  boiling 
water.  If  the  melted  fat  after  filtering  is  not  perfectly  clear,  it 
must  be  filtered  a  second  time.  Preserve  the  fat  in  a  stoppered 
bottle  which  should  be  kept  in  a  cool  dark  place. 

Note.  —  By  exercising  care,  the  fat  may  also  be  filtered  through 
clean,  dry  absorbent  cotton. 


io6 


QUANTITATIVE  ANALYSIS 


PHYSICAL  TESTS 

The  Determination  of  the  Specific  Gravity  of  Butter  Fat 

Procedure.  —  Clean  a  specific  gravity  flask  of  25  c.c.  capacity 
(see  Fig.  28)  by  washing  thoroughly  with  hot  water,  alcohol,  and 
ether.  Dry  the  flask  and  stopper,  cool  in  a  desiccator,  and  weigh 
accurately.  Fill  the  flask  with  cold,  recently  boiled,  distilled  water. 

Insert  the  stopper  and  allow  to  stand  for 
30  minutes  in  a  bath  of  distilled  water 
kept  at  37.8°.  Remove  the  flask  from 
the  bath,  wipe  dry,  and  after  it  has  cooled 
nearly  to  room  temperature,  place  it  in 
the  balance  case  and  weigh  when  the 
balance  temperature  has  been  reached. 
Rinse  the  flask  with  alcohol  and  ether, 
dry  thoroughly,  and  fill  it  with  the 
freshly  filtered  fat  from  a  vessel  which 
has  been  standing  in  the  bath  at  37.8°. 
Replace  the  flask  in  the  water  bath,  main- 
tain for  fifteen  minutes  at  the  tempera- 
ture 37.8°,  and  proceed  as  with  the  water. 
The  weight  of  the  fat  having  been  deter- 
mined, the  specific  gravity  is  obtained  by  dividing  it  by  the 
weight  of  water  previously  found. 

Notes.  —  i.  At  the  temperature  35°  C.  it  has  been  found  that  the 
difference  between  the  specific  gravity  of  butter  fat  and  certain 
other  fats  is  greater  than  at  any  other  temperature.  A  sample  of 
butter  fat  at  100°  C.  gave  a  specific  gravity  of  0.8672,  oleomargarine 
0.8598,  a  difference  of  0.0074.  At  35°  the  specific  gravity  of  the 
same  butter  fat  was  0.9121,  the  oleomargarine  0.9019,  a  difference 
of  0.0102.  The  temperature  37.8°  (100°  F.)  has  been  selected  for 
this  determination,  because  at  this  temperature  all  the  fats  used  for 
the  adulteration  of  butter  remain  liquid.  At  a  lower  temperature 
there  is  danger  of  solidification. 

In  some  laboratories  it  is  customary  to  carry  out  this  determina- 
tion at  100°  C. 

2.  A  number  of  tests  carried  out  by  J.  Bell  show  the  values  of 
the  specific  gravities  of  butter  and  certain  other  fats.  His  results 
are  incorporated  in  the  following  table  : 


FIG.  28 


AGRICULTURAL  ANALYSIS  107 


KIND  OF  FAT 

SPECIFIC  GRAVITY  AT 
37-8° 

Butter  fa,t  (\i'\  samples}                        

O.QI  I—  O  QI"? 

O  QO3Q 

0.0028^ 

Beef  suet                            

O.QO772 

O.QO^84 

It  is  obvious  that  an  oil  with  a  high  specific  gravity  such  as 
cocoanut  oil  (0.9167  at  37.8°)  could  be  mixed  with  oleomargarine, 
and  the  adulteration  could  not  be  detected  in  this  manner. 

The  Determination  of  the  Melting  Point 

(  Wiley's  Method) 

Apparatus  and  Reagents.  —  Obtain  an  accurate  thermometer  which 
reads  easily  to  tenths  of  a  degree,  a  tall  beaker  about  35  cm.  high 
and  10  cm.  in  diameter,  two  test  tubes  about  30  cm.  long  and  3.5 
cm.  in  diameter.  Place  the  beaker  upon  an  asbestos  gauze  which  is 
supported  by  the  ring  of  an  iron  stand.  By  means  of  a  clamp  suspend 
the  test  tube  so  that  it  extends  to  within  a  few  centimeters  of  the 
bottom  of  the  beaker.  Suspend  the  thermometer  in  such  a  way 
that  it  can  be  easily  lowered  into  the  test  tube.  Arrange  a  bent 
glass  tube  so  that  it  will  extend  to  the  bottom  of  the  beaker,  and 
make  possible  the  agitation  of  the  liquid  by  blowing  air  through 
the  tube. 

Procedure.  —  Pour  freshly  boiled  hot  water  into  the  test  tube  until 
it  is  nearly  half  full.  Nearly  fill  it  with  hot  freshly  boiled  alcohol 
which  should  be  carefully  poured  down  the  side  of  the  inclined 
tube  to  avoid  too  much  mixing,  and  place  into  a  tall  beaker  con- 
taining ice  water. 

Prepare  several  disks  of  fat  by  allowing  the  melted  and  filtered 
fat  to  fall  from  a  dropping  tube  from  a  height  of  1 5-20  cm.  upon 
a  smooth  piece  of  ice  floating  in  recently  boiled  distilled  water, 
forming  disks  from  I  to  1.5  cm.  in  diameter.  By  pressing  the  ice 
under  water,  the  disks  are  made  to  float  on  the  surface,  from  which 
they  can  be  removed  easily  with  a  cold  steel  spatula.  Drop  the 
disk  of  fat  into  the  test  tube.  When  it  has  come  to  rest,  place  the 
test  tube  into  the  beaker  on  the  stand  and  lower  the  delicate  ther- 


108  QUANTITATIVE  ANALYSIS 

mometer  until  the  fat  particle  is  even  with  the  center  of  the  bulb. 
Nearly  fill  the  beaker  with  distilled  water,  and  heat  the  water 
slowly,  keeping  it  stirred  by  occasionally  blowing  through  the  bent 
tube.  When  the  temperature  of  the  mixture  rises  to  about  6°  below 
the  melting  point,  the  disk  of  fat  begins  to  shrivel,  and  gradually 
rolls  up  into  an  irregular  mass.  The  rise  of  temperature  should  be 
so  regulated  that  the  last  two  degrees  of  increment  require  about 
ten  minutes.  As  soon  as  the  mass  of  fat  forms  a  sphere,  read  the 
temperature,  remove  the  test  tube  from  the  bath  and  place  it  into 
the  beaker  of  ice  water.  A  second  tube  containing  alcohol  and 
water  should  be  placed  at  once  into  the  bath  and  the  determination 
repeated.  As  this  test  tube  has  been  standing  in  ice  water,  its 
temperature  is  low  enough  to  cool  the  bath  sufficiently.  Triplicate 
determinations  should  be  made  and  the  second  and  third  results 
should  agree  within  0.2°. 

Notes. —  i.  If  the  alcohol  is  added  after  the  water  has  cooled, 
the  mixture  will  contain  air  bubbles  which  will  gather  on  the  disk 
of  fat  as  the  temperature  rises  and  may  finally  force  it  to  the 
top. 

2.  The  edge  of  the  disk  should  not  be  allowed  to  touch  the  sides 
of  the  tube.     If   this   happens,  a   new  determination   should   be 
made. 

3.  In  general  the  melting  point  of   butter   is  several  degrees 
higher  than  that  of  oleomargarine,  although  artificial  butters  may 
be   made   which    have   the    same  melting  point  as  butter.     Con- 
sequently, this  determination  is  not  of  itself  conclusive  evidence 
of  the  purity  of  the  sample,  but  is  of  value  only  when  used  to  sup- 
plement other  tests.     The  following  table  gives  the  melting  points 
of  some  of  the  more  common  fats : 


FATS 

MELTING  POINT 

Butter         .           ... 

28-^°  C. 

Oleomargarine  (mean)                 ...          ... 

26 

Oleo  oil      ....          .                          .... 

33—  3Q 

Beef  tallow     ....                               .... 

4.2—  4.Q 

Mutton  tallow      ...               .                    ... 

44.—  Co 

Lard      

•26—4.6 

AGRICULTURAL  ANALYSIS 


109 


CHEMICAL  TESTS 

It  will  be  found  advantageous  to  weigh  out  at  the  same  time 
samples  for  the  following  determinations  :  volatile  acids,  saponi- 
fication  number,  insoluble  acids,  and  iodine  absorption. 

Obtain  a  tube  of  the  form  shown  in  Fig.  29  for  weighing  samples 


[ 

fff 

r_— 

25. 

20. 

15. 

10 

FIG.  29 


of  butter  fat.  Nearly  fill  it  with  clear  molten  fat,  weigh,  and  re- 
move samples  by  blowing  the  fat  into  the  proper  receptacle  as  with 
a  wash  bottle.  In  order  to  prevent  moisture  from  the  breath 
entering  the  tube,  place  on  the  short  tip  the  mouthpiece  A,  which 
is  filled  with  soda  lime.  Remove  the  mouthpiece  and  reweigh. 
Take  all  of  the  samples  in  this  manner. 


1 10  QUANTITATIVE  ANALYSIS 

The  Determination  of  the  Volatile  Fatty  Acids 

(Reichert-Meissl  Method) 

Principle.  —  If  a  fat  or  oil  is  heated  with  an  alkali,  the  glycerides 
present  are  broken  up,  with  the  formation  of  glycerin  and  the 
alkali  salts  of  the  fatty  acids.  These  salts  are  known  as  soaps,  and 
the  process  is  called  saponification.  The  following  equation  shows 
the  reaction  by  which  stearin  is  saponified : 

stearin  sodium  stearate  glycerin 

(C17H35COO)3C3H5  +  3  NaOH  =  3  C17H35COONa  +  C3H6(OH)3. 

The  addition  of  dilute  sulphuric  acid  to  the  soap  solution  liberates 
the  fatty  acids. 

stearic  acid 

2  C17H35COONa  +  H2SO4  =  2  C17H35COOH  +  Na2SO4. 

On  adding  water  and  distilling,  the  volatile  fatty  acids  pass  over 
with  the  steam,  are  condensed,  and  may  be  estimated  by  titration 
with  a  standard  alkali. 

The  number  of  cubic  centimeters  of  N/io  sodium  hydroxide 
solution  equivalent  to  the  soluble  fatty  acids  distilled  from  five 
grams  of  the  fat  under  the  conditions  of  the  experiment  is  known 
as  the  Reichert-Meissl  Number. 

Procedure.  —  Weigh  samples  of  5  grams  of  the  fat  into  two 
250  c.c.  Erlenmeyer  flasks,  in  the  manner  above  described.  Add 
10  c.c.  of  95  per  cent  alcohol  and  2  c.c.  of  sodium  hydroxide  solution 
( i  :  i ),  attach  a  reflux  condenser,  consisting  of  a  glass  tube  about 
one  meter  in  length,  to  the  neck  of  the  flask  by  means  of  a  rubber 
stopper,  and  heat  on  the  water  bath  with  occasional  shaking  until 
the  saponification  is  complete.  This  is  shown  by  the  clearness  of 
the  solution  and  its  freedom  from  fat  globules.  Evaporate  the 
alcohol  by  removing  the  condenser  and  heating  the  flask  on  the 
steam  bath.  The  last  traces  of  alcohol  vapor  may  be  removed  by 
waving  the  flask  briskly,  mouth  down,  to  and  fro.  Dissolve  the 
soap  by  adding  132  c.c.  of  recently  boiled  distilled  water  to  the 
flask  and  warming  on  the  steam  bath,  with  occasional  shaking, 
until  solution  is  complete.  When  the  soap  solution  has  cooled  to 
about  60°,  set  the  fatty  acids  free  by  adding  8  c.c.  of  dilute  sul- 
phuric acid  solution  (200  c.c.  of  concentrated  sulphuric  acid  in 
1000  c.c.  of  water).  Connect  the  flask  with  the  reflux  condenser 


AGRICULTURAL  ANALYSIS  III 

and  heat  in  the  water  bath  without  boiling,  until  the  fatty  acid 
emulsion  forms  an  oily  layer  on  the  surface  of  the  liquid.  Cool 
the  flask  to  room  temperature  and  add  a  few  pieces  of  pumice 
stone  to  prevent  bumping.  The  pumice  stone  is  prepared  by 
throwing  it,  at  a  white  heat,  into  distilled  water,  and  keeping  it 
under  water  until  used.  This  treatment  expels  the  air  from  the 
pores  of  the  pumice  stone,  so  that  it  will  sink  when  added  to  the 
liquid.  Connect  the  flask  with  a  glass  condenser  and  distill  at 
such  a  rate  that  no  c.c.  of  the  distillate  will  be  collected  in 
thirty  minutes.  Collect  the  distillate  in  a  no  c.c.  graduated  flask, 
in  the  neck  of  which  is  a  short  funnel  provided  with  a  loose  tuft  of 
absorbent  cotton  to  serve  as  a  filter.  Pour  the  distillate  into  a 
beaker,  add  0.5  c.c.  of  phenolphthalein  solution,  and  titrate  with 
N/io  sodium  hydroxide  solution  until  the  red  color  produced  re- 
mains unchanged  for  two  or  three  minutes.  Calculate  the  Reichert- 
Meissl  number. 

Note. —  i.  The  volatile  acids  are  defined  as  those  which  pass 
over  with  steam,  irrespective  of  the  boiling  point  of  the  acid. 
The  entire  amount  of  the  volatile  fatty  acids  is  not  obtained  in  the 
above  process ;  moreover,  the  quantity  varies  with  the  amount  of 
distillate,  the  concentration  of  reagents  used,  and  other  factors. 

2.  The  alcohol  added  assists  in  the  solution  of  the  fat  and  con- 
sequently gives  a  more  rapid  saponification. 

3.  A  study  of  the  errors  of  the  Reichert-Meissl  process   has 
been  made  by  Wollny.     He  has  found  them  to  be  : 

a.  The  absorption  of  carbon  dioxide  during  saponification. 

b.  The  formation  of  volatile  ethers  during  saponification.     Bu- 
tyric acid,  for  example,  reacts  with  alcohol  to  form  volatile  ethyl 
butyrate : 

C3H7COOH  +  C2H6OH  =  C3H7COOC2H5  +  H2O. 

The  escape  of  the  ethyl  butyrate  is  prevented  by  the  reflux  con- 
denser and  it  is  finally  saponified. 

c.  The  formation  of  ethers  during  the  distillation. 

d.  The  retention  of  some  of  the  volatile  acids,  owing  to  cohesion 
of  the  fatty  acids. 

e.  Variation  in  the  fraction  of  the  volatile  fatty  acids  distilled, 
owing  to   size   and   shape   of  the   distilling   vessel,    and    to   the 
length  of  time  of  the  distillation. 


112  QUANTITATIVE  ANALYSIS 

By  the  adoption  of  standard  methods  of  procedure,  the  above 
errors  have  either  been  minimized  or  made  constant,  so  that 
uniform  results  may  be  obtained,  which  permits  the  use  of  this 
method  as  one  of  comparison. 

4.  The  determination  of  the  volatile  acids  is  one  of  the  most 
common  and  the  most  important  methods  for  the  determination  of 
the  adulteration  of  butter  with  foreign  fats.  Not  only  does  it 
serve  for  their  detection,  but  it  is  also  of  use  in  the  estimation  of 
the  amount  of  foreign  fat  which  has  been  added  to  the  butter. 

The  following  table,  compiled  by  Blyth,  shows  the  Reichert-Meissl 
number  of  butter  fat  compared  with  other  fats  : 


KIND  OF  FAT 

REICHERT  MEISSL 
NUMBER 

Butter  fat      

24—  32 

Butter  fat  +  10  per  cent  cocoanut  oil   

26  8 

18  o 

Butter  fat           50      per  cent] 
Cocoanut  oil      22.5   per  cent  \     

17  A. 

Oleomargarine  27.5   per  cent] 
Cocoanut  oil      

7o8o 

Oleomargarine  

o  8—3  o 

Lard     . 

o  4—0  6 

Olive  oil   

o  6 

The  Determination  of  the  Soluble  and  the  Insoluble  Fatty  Acids 

Principle.  —  The  fatty  acids  in  the  butter  fat  may  be  set  free  by 
saponification  and  treatment  of  the  soap  with  a  known  amount  of 
standard  acid,  as  in  the  determination  of  the  volatile  acids.  On 
melting  the  fatty  acids,  leaching  with  water,  and  cooling  to  zero 
degrees,  the  insoluble  acids  adhere  and  form  a  solid  cake  from 
which  the  soluble  fatty  acids  may  be  separated  by  filtration,  and 
determined  by  titration.  The  insoluble  acids  may  be  weighed 
directly. 

Soluble  Acids 

Procedure.  —  Place  two  5  gram  samples  in  250  c.c.  Erlenmeyer 
flasks,  add  from  a  pipette  50  c.c.  of  alcoholic  potash  solution  (40 
grams  of  potassium  hydroxide  in  one  liter  of  95  per  cent  redistilled 
alcohol),  and  saponify  as  in  the  determination  of  volatile  acids.  Two 


AGRICULTURAL  ANALYSIS  113 

blank  experiments  should  be  conducted  at  the  same  time.  After 
complete  saponification  remove  the  condensers  from  the  flasks  and 
evaporate  the  alcohol  by  further  heating.  Titrate  the  blanks  with 
half  normal  hydrochloric  acid,  using  phenolphthalein  as  an  indica- 
tor. Run  into  each  of  the  flasks  containing  the  saponified  fat  one 
cubic  centimeter  more  of  the  half  normal  hydrochloric  acid  than 
was  found  necessary  to  neutralize  the  alkali  in  the  blanks.  Connect 
with  the  reflux  condenser,  and  heat  on  the  steam  bath  until  the 
separated  fatty  acids  have  collected  in  a  layer. 

Cool  the  flask  in  ice  water  until  the  fatty  acids  have  solidified, 
then  decant  the  liquid  through  a  dry  filter,  taking  care  not  to  break 
the  cake.  Add  about  200  c.c.  of  water  to  the  flask,  insert  the 
cork  with  the  condenser,  and  heat  on  the  steam  bath  until  the  cake 
of  acids  is  thoroughly  melted.  During  the  process  the  flask  should 
occasionally  be  agitated  with  a  circulatory  motion  in  such  a  way 
that  its  contents  are  not  allowed  to  touch  the  cork.  When  the 
fatty  acids  have  again  separated  into  an  oily  layer,  cool  the  flask 
and  contents  in  ice  water,  and  filter  the  liquid  through  the  same 
filter  into  the  liter  flask  as  before.  Repeat  the  treatment  with  hot 
water,  followed  by  cooling  and  filtration  of  the  wash  water,  three 
times,  adding  the  washings  to  the  first  filtrate.  Make  up  the  wash- 
ings with  water  to  the  liter  mark,  mix,  and  titrate  100  c.c.  portions 
with  N/io  sodium  hydroxide  solution,  using  the  proper  indicator. 
Calculate  the  amount  of  alkali  equivalent  to  the  total  amount  of 
solution.  This  represents  the  volume  of  N/io  sodium  hydroxide 
neutralized  by  the  soluble  fatty  acids  of  the  butter  fat,  plus  that 
corresponding  to  the  excess  of  one  cubic  centimeter  of  N/2  hydro- 
chloric acid  used.  Deduct  from  the  total  amount  the  number  of 
cubic  centimeters  of  the  standard  alkali  equivalent  to  this  excess 
of  acid,  and  from  the  corrected  volume  of  standard  alkali  used 
calculate  the  percentage  of  soluble  fatty  acids  in  the  butter  fat 
as  butyric  acid. 

Insoluble  Acids 

Procedure.  —  Allow  the  flask  containing  the  cake  of  insoluble 
acids  and  the  paper  used  for  the  filtration  of  the  soluble  acids  to  drain 
for  twelve  hours,  than  transfer  the  cake  with  as  much  of  the  fatty 
acids  as  can  be  removed  from  the  filter  paper  to  a  weighed  glass 
evaporating  dish.  Place  the  filter  in  the  Erlenmeyer  flask  and  wash 
it  thoroughly  with  strong  alcohol,  transferring  all  the  washings  to 


114 


QUANTITATIVE  ANALYSIS 


the  dish.  Evaporate  the  alcohol  by  placing  the  dish  upon  the 
water  bath,  dry  the  dish  in  the  water  oven  for  two  hours,  cool  in  the 
desiccator,  and  weigh.  Heat  again  for  half  an  hour,  cool  and 
weigh.  If  a  considerable  loss  in  weight  is  found,  heat  for  an 
additional  half  hour.  From  the  data  calculate  the  percentage  of 
insoluble  fatty  acids  in  the  butter  fat. 

Note.  —  The  above  determination  gives  a  valuable  indication  of 
the  presence  of  foreign  fats  in  butter,  since  the  fats  used  for  -the 
purpose  of  adulteration  contain  a  high  percentage  of  insoluble  acids. 

Blyth  gives  the  following  results  of  analyses  which  show  the 
relative  amounts  of  soluble  and  insoluble  acids  in  pure  and  adul- 
terated butters. 


KINDS  OF  BUTTER 

PERCENTAGE  OF  FATTY  ACIDS 

Soluble 

Insoluble 

Genuine 
Butters 

Adulterat 
Butters 

j 

5.92 
5.76 

5-37 
4-77 

1.98 

2-34 
0.58 

87.86 

88.10 
87.68 
88.44 

93-30 
93.82 

95-51 

II                             

Ill                                ... 

IV    

c\ 

ed!  ii  ' 

llir. 

Saponification  or  Koettstorfer  Number 

Principle.  —  The  amount  of  alkali  necessary  to  saponify  any  fat 
depends  upon  the  glycerides  which  compose  the  fat.  In  the 
case  of  the  pure  glycerides,  the  smaller  the  number  of  carbon 
atoms  present  in  the  acid,  the  more  alkali  will  be  required  for 
Saponification,  as  may  be  seen  from  the  following  equations : 

butyrin 

(C3H7COO)3C3H6  +  3  KOH  =  3  C3H7COOK  +  C3H5(OH)3. 
(mol.  wt.  302)    (3  x  m.  w.  =  168) 

One  gram  of  butyrin  requires  0.556  gram  of  potassium  hydroxide. 

stearin 

(C17H36COO)3C,H6  +  3  KOH  =  3  C17H36COOK  +  C8H6(OH)3. 
(mol.  wt.  891)      (3  x  m.  w.  =  168) 


AGRICULTURAL  ANALYSIS  115 

One  gram  of  stearin  requires  0.189  gram  of  potassium  hy- 
droxide. 

From  the  above,  it  is  obvious  that  a  fat  like  butter,  containing 
a  considerable  quantity  of  glycerides  with  a  small  number  of 
carbon  atoms,  will  require  more  alkali  for  saponification  than  a  fat 
which  is  composed  of  the  higher  glycerides. 

The  number  of  milligrams  of  potassium  hydroxide  necessary  to 
completely  saponify  one  gram  of  the  fat  is  called  the  Saponifica- 
tion Number.  To  determine  this  value  a  definite  amount  of  the 
fat  is  heated  with  standard  alkali,  and  after  the  saponification  the 
excess  of  alkali  is  determined  by  titration  with  standard  acid. 

Procedure.  —  Place  samples  of  one  or  two  grams  of  the  butter  fat 
into  Erlenmeyer  flasks,  add  25  c.c.  of  alcoholic  potash  solution 
(40  grams  of  potassium  hydroxide  in  one  liter  of  95  per  cent 
redistilled  alcohol),  connect  with  a  reflux  condenser,  and  saponify 
by  heating  on  the  water  bath.  Two  blank  experiments  should  be 
conducted  at  the  same  time.  As  soon  as  saponification  is  complete, 
remove  the  flasks  from  the  bath,  cool,  and  titrate  the  samples  and 
also  the  blanks  with  half-normal  hydrochloric  acid,  using  phenol- 
phthalein  as  an  indicator.  Subtract  from  the  number  of  cubic  centi- 
meters of  acid  used  to  titrate  the  blank  that  necessary  to  titrate 
the  excess  of  alkali  from  the  saponification.  This  gives  the  num- 
ber of  cubic  centimeters  of  acid  equivalent  to  the  alkali  used  for 
the  saponification.  Calculate  the  saponification  number. 

Notes.  —  i.  The  following  are  the  values  of  the  saponification 
number  of  some  of  the  more  common  fats : 

SAPONIFICATION  NUMBER 

Butter  fat 220-233 

Oleomargarine  (mean)       .     .     195.5 

Cocoanut  oil 257.3 

Tallow 196.8 

Commercial  lard       .     .     .     .     195.0 

2.  It  has  been  suggested  by  Allen  that  the  results  obtained  by 
the  above  method  be  expressed  in  terms  of  the  "  saponification 
equivalent."  This  is  the  number  of  grams  of  fat  which  react  with 
one  gram  molecule  of  the  alkali  used,  and  is  really  an  expression 
of  the  mean  molecular  weight  of  the  fat.  The  saponification 
equivalent  has  the  advantage  that  it  is  independent  of  the  kind  of 
alkali  used  for  saponification 


1 1 6  QUANTITATIVE  ANAL YSIS 

3.  The  alcoholic  potash  used  in  the  saponification  undergoes 
changes  other  than  that  represented  by  its  reaction  with  the  fat. 
For  example,  some  of  it  reacts  with  the  glass  vessel  in  which  the 
reaction  takes  place.  For  this  reason,  the  solution  used  for  deter- 
mining the  strength  of  the  caustic  potash  must  be  subjected  to 
exactly  the  same  treatment  (length  of  time  of  heating,  etc.)  as 
the  alkali  used  for  the  saponification ;  hence  the  necessity  of  the 
blank. 

The  Determination  of  the  Iodine  Absorption  Number 

(Hamis  Method) 

Principle.  —  This  determination  is  based  on  the  fact  that  unsatu- 
rated  fatty  acids  react  with  the  halogens  to  form  addition  products. 
Olein,  for  example,  reacts  with  iodine  according  to  the  equation 

olein  di-iodo-stearin 

(C17H38COO)3C3H6  +  3  I,  =  (C17H33I2COO)3C8H5. 

Since  different  fats  and  oils  contain  different  amounts  of  the 
unsaturated  compounds,  the  determination  of  the  amount  of  halo- 
gen absorbed  is  of  value  as  a  means  of  identification. 

The  method  in  outline  consists  in  adding  a  definite  amount  of 
the  halogen  to  a  solution  of  the  fat,  and  titrating  the  excess  after 
standing  for  a  definite  length  of  time.  In  the  Hanus  method  the 
halogen  used  is  a  solution  of  iodine  monobromide.  The  amount 
of  halogen  absorbed  is  calculated  as  iodine.  The  number  of  grams 
of  iodine  absorbed  by  100  grams  of  the  fat  is  cilled  the  Iodine 
Absorption  Number. 

Reagents 

Preparation  of  iodine  monobromide  solution.  Dissolve  13.2 
grams  of  pure  resublimed  iodine  in  one  liter  of  pure  glacial  acetic 
acid  (99  per  cent),  heating  the  solution  if  necessary.  To  the  cold 
solution  add  3  c.c.  of  liquid  bromine.  This  reagent  remains  un- 
changed for  months. 

Sodium  thiosulphate  solution.  —  Standardize  an  approximately 
N/io  sodium  thiosulphate  solution  against  a  standard  solution  of 
potassium  dichromate  in  the  manner  described  in  Exercise  XXVII, 
page  82. 

Starch  Solution.  —  Prepare  according  to  directions  given  on 
page  80. 


AGRICULTURAL  ANALYSIS  117 

Procedure.  —  Place  two  portions  of  0.7-1  gram  of  the  butter  fat 
into  narrow-mouthed  bottles  of  about  250  c.c.  capacity,  which  are 
provided  with  well-ground  glass  stoppers.  Dissolve  the  fat  by 
adding  10  c.c.  of  chloroform,  and  after  solution  has  taken  place, 
add  30  c.c.  of  the  iodine  monobromide  solution  (accurately  meas- 
ured), place  the  bottle  in  the  dark,  and  allow  to  stand  for  about 
forty  minutes.  Two  blanks  should  be  carried  on  at  the  same  time 
and  under  the  same  conditions  as  the  above  determination.  On 
account  of  the  high  coefficient  of  expansion  of  acetic  acid,  the 
iodine  solution  should  be  measured  at  the  same  temperature  for 
the  blanks  as  for  the  determination.  If  the  deep  brown  color 
should  be  discharged  on  standing,  25  c.c.  more  of  the  iodine  solu- 
tion should  be  added. 

Add  to  the  bottle  100  c.c.  of  distilled  water,  and  20  c.c. 
of  potassium  iodide  solution  (150  grams  per  liter).  Any  iodine 
which  may  be  noticed  on  the  stopper  of  the  bottle  should  be 
washed  back  into  the  bottle  with  the  potassium  iodide  solution. 
Titrate  the  iodine  in  the  bottle  with  sodium  thiosulphate  solu- 
tion, running  it  in  gradually  with  constant  shaking  until  the  yel- 
low color  of  the  solution  has  almost  disappeared.  Add  a  few 
drops  of  starch  solution  and  continue  the  titration  until  the 
solution  is  colorless.  Towards  the  end  of  the  reaction  the  bottle 
should  be  stoppered  and  violently  shaken,  so  that  any  iodine  re- 
maining in  solution  in  the  chloroform  may  be  taken  up  by  the  po- 
tassium iodide  solution.  The  number  of  cubic  centimeters  of 
thiosulphate  solution  used  in  the  blank  minus  that  used  in  the  de- 
termination gives  the  thiosulphate  equivalent  to  the  amount  of 
iodine  absorbed.  From  the  data  calculate  the  iodine  absorption 
number. 

Notes. —  i.  It  is  customary  to  calculate  the  absorption  in  terms 
of  iodine,  although  it  is  obvious  that  the  bromine  may  take  an 
equally  active  part  in  the  reaction. 

2.  The  absorption  of  iodine  and  bromine  is  due  mainly  to  their 
addition  to  the  unsaturated  acid.     Certain  secondary  reactions  oc- 
cur, however,  in  which  the  halogens  are  used  up.     Chief  among 
these  is  the  substitution  of  the  iodine  or  bromine  in  the  chains  of 
the   fatty  acids.     This  determination  is,  therefore,    not  an    exact 
quantitative  measure  of  the  unsaturated  acids. 

3.  The  following  table  shows  the  iodine  absorption  numbers  of 


n8  QUANTITATIVE  ANALYSIS 

some  of  the  more  common  fats.     The  majority  of  these  numbers 
were  determined  by  Tolman  and  Munson. 


KIND  OF  FAT 

IODINE  NUMBER 

Butter  fat   

26  38 

Oleomargarine     

C2    f)C 

Oleo  oil       

5^  °5 
A->  -j 

Olive  oil      

43-3 
84  6 

Linseed  oil       

17  1     178 

I/I      1/0 

Household  Tests 

Certain  simple  household  tests  for  the  identification  of  butter 
have  been  found  after  a  little  practice  to  give  reliable  results  and 
have  consequently  been  introduced  into  food  laboratories. 

The  Foam  Test 

This  is  used  to  distinguish  pure  butter  from  process  butter  and 
oleomargarine. 

Procedure.  —  Place  from  3  to  5  grams  of  the  sample  into  a 
test  tube,  or  a  large  spoon,  and  heat  over  a  low  Bunsen  flame,  stir- 
ring constantly.  If  more  convenient,  the  spoon  may  be  held  above 
the  chimney  of  an  ordinary  kerosene  lamp,  or  over  an  ordinary 
gas  jet.  If  the  sample  is  fresh  butter,  it  will  boil  quietly  with  the 
evolution  of  many  small  bubbles  throughout  the  mass,  which  pro- 
duce a  large  amount  of  foam.  Oleomargarine  and  process  butter 
foam  either  very  slightly  or  not  at  all,  and  sputter  and  crackle  like 
hot  grease  containing  water. 

Another  point  of  distinction  is  noted  if  a  small  portion  of  the 
sample  be  placed  into  a  small  bottle  and  set  into  a  vessel  of  water 
sufficiently  warm  to  melt  the  butter.  The  sample  is  kept  melted 
from  half  an  hour  to  an  hour,  and  then  examined.  If  renovated 
butter  or  oleomargarine,  the  fat  will  be  turbid ;  while  if  genuine 
fresh  butter,  the  fat  will  almost  certainly  be  clear. 

The    Waterhouse  or  Milk  Test 

This  serves  to  distinguish  oleomargarine  from  fresh  and  process 
butter.  It  is  based  on  the  fact  that  molten  butter  fat,  if  added  to 
milk  and  cooled,  will  be  found  diffused  with  the  milk  fat,  owing  to 


AGRICULTURAL  ANALYSIS      .  119 

its  similarity  to  the  latter.  Oleomargarine,  on  the  contrary,  being 
made  from  foreign  fats,  will  not  diffuse  under  these  conditions,  but 
will  remain  in  a  mass. 

Procediire.  —  Place  about  50  c.c.  of  well-mixed  sweet  milk  into  a 
beaker,  heat  nearly  to  boiling,  add  5  or  10  grams  of  the  sample, 
and  stir  with  a  splinter  of  wood  until  the  fat  is  melted.  Place  the 
beaker  into  a  dish  of  ice  water  and  begin  stirring  before  the  fat 
starts  to  solidify,  which  takes  place  in  ten  or  fifteen  minutes,  and 
continue  until  the  fat  becomes  solid.  If  the  sample  is  butter, 
either  fresh  or  renovated,  it  will  be  solidified  in  a  granular  condi- 
tion, and  distributed  through  the  milk  in  small  particles.  If  the 
sample  consists  of  oleomargarine,  it  solidifies  practically  in  one 
piece,  and  may  be  lifted  from  the  milk  by  means  of  the  stirrer. 

The  nature  of  the  sample  under  examination  may  be  deter- 
mined by  these  two  tests.  The  first  distinguishes  fresh  butter 
from  renovated  butter  and  oleomargarine,  while  the  second  dis- 
tinguishes oleomargarine  from  either  fresh  butter  or  renovated 
butter. 

REFERENCES 

LEACH,  A.,  Food  Inspection  and  Analysis,  Chapter  XII,  p.  368. 
LEWKOWITSCH,  J.,  Chemical  Analysis  of  Oils,  Fats,  and  Waxes. 

THE  ANALYSIS   OF  CEREALS   AND   FEEDING  MATERIALS 

These  food  stuffs  may  be  conveniently  classified  as  follows : 

1.  Cereals,  occurring  in  the  natural  state,  of  which  corn,  oats, 
and  wheat  are  types. 

2.  Cereal  products,  obtained  from  cereals  by  a  certain  amount  of 
preparation.     To  this  class  belong  flour,  breakfast  foods,  etc. 

3.  Feeding  materials,  including  such  substances  as  hay,  silage, 
also   oil    cake,  dried   sugar-beet   pulp,  and  other   industrial  by- 
products. 

Composition 

Vegetable  foods,  in  general,  contain  high  percentages  of  car- 
bohydrates and  comparatively  low  percentages  of  proteids  and 
fats.  There  are  certain  exceptions,  as  in  the  case  of  leguminous 
foods  such  as  peas  and  beans,  which  contain  high  percentages  of 
proteid  matter.  Moreover,  cotton,  rape,  and  certain  other  seeds 
contain  large  amounts  of  fats  and  oils. 


I2O 


QUANTITATIVE  ANALYSIS 


The  following  table  shows  the  composition  of  some  of  the  more 
common  vegetable  foods : 


WATER 

PROTEIDS 

FAT 

SUGAR 

GUM  AND 
DEXIRIN 

STARCH 

CRUDE 
FIBER 

ASH 

Quaker  Rolled  Oats    .     . 
Oats 

9.40 

17-55 

7.20 





61.56! 

2.40 

1.89 

Wheat  

ID  6^ 

12  3^ 

o2 

1.91 

1.79 

0    o» 

54.08 
f\A  nft 

Corn     . 

9gt 

••/a 

A  6'2 

••••45 

.2.30 

o  O0 

2-53 

Peas      

12  4.O 

20  68 

4-u^s 

3-3° 

62.57 

CO    rr>  1 

2.49 

i-S1 

r>  9,9. 

Beans 

5°-52 
-f.  -„  \ 

4.21 

Cotton-seed  meal    . 
Sugar-beet  pulp  2    .     .     . 

8.20 

88-53 

42.30 

9-45 

13.10 

0.68 





50-77  x 

23.60! 
62.62  1 

3-54 
5-60 
22.40 

3-29 

7-20 
4-85 

1  Nitrogen-free  extract,  obtained  by  difference. 


2  Dry  matter  basis. 


Carbohydrates 

The  food  values  of  the  carbohydrates  present  in  vegetable  foods 
depend  to  a  great  extent  upon  their  solubilities  or  ease  of  con- 
version to  soluble  forms.  The  carbohydrates  may  be  classified 
according  to  these  properties : 

1.  Those  soluble  in  water,  of  which  the  sugars  and  dextrin  are 
the  most  important. 

2.  Those  which  are  not  easily  soluble  in  water,  but  which  are 
made  soluble  by  the  action  of  certain  ferments  or  by  hydrolysis 
with  acid.     Starch  is  the  most  important  member  of  this  class. 

3.  Carbohydrates  which  resist  the  action  of  the  usual  reagents. 
They  are  not  hydrolyzed  either  by  acid  or  alkali,  but  remain  as 
fiber  in  the  residue  after  treating  the  substance  with  these  reagents. 
Cellulose  is  a  type  of  this  class. 

4.  Certain  insoluble  carbohydrates,  which  on  being  hydrolyzed 
with  an  acid  yield  sugars.     The  members  of  this  class  are  often 
called  "hemicellulose."     The  greater  portion  of   these  insoluble 
carbohydrates  are  pentosans.     The  class  is  of  comparatively  small 
importance. 

In  the  analysis  of  agricultural  products  the  carbohydrates  are 
often  determined  by  difference,  being  included  in  what  is  known 
as  the  Nitrogen-free  Extract.  This  is  the  residue  left  after  the 
determination  of  proteids,  ether  extract,  ash,  moisture,  and  crude 
fiber.  Since  it  contains  such  substances  as  gums,  resins,  etc.,  it 
approximates  but  roughly  the  total  carbohydrates  present. 


AGRICULTURAL  ANALYSIS 


121 


The  following  table,  containing  the  results  of  a  series  of  analy- 
ses by  Stone,  shows  the  percentages  of  the  various  carbohydrates 
in  certain  of  the  more  common  cereals  and  cereal  products : 


SUCROSE 

INVERT 
SUGAR 

DEX- 
TRIN 

SOLUBLE 
STARCH 

NORMAL 
STARCH 

PENTO- 

SANS 

CRUDE 
FIBER 

Wheat  flour  

0.18 

O.OO 

O.OO 

O.OO 

46.IQ 

O.OO 

O.2C 

Corn     

O.27 

O.OO 

O.32 

O.OO 

42.  CO 

c.14 

I  QQ 

i.yy 

Su°"ar  beet 

8.^8 

O.O7 

o.^c 

O.OO 

O.OO 

4.80 

I  OO 

Bread  (wheat)   .... 

0.05 

0.32 

0.68 

i-37 

27-93 

4.16 

2.70 

Corn  cake  (maize).     .     . 

0.16 

O.IQ 

0.00 

2.80 

40.37 

3-54 

2.22 

Fats.  —  The  fatty  material  present  in  vegetable  foods  is  a  complex 
mixture  of  glycerides.  Olein,  stearin,  and  palmitin  are  always 
present  to  a  greater  extent  than  the  other  glycerides. 

Proteids. — The  proteidsof  the  vegetable  foods  vary  considerably 
both  as  to  character  and  to  the  amount  present.  For  the  classifi- 
cation and  general  methods  of  separation  of  the  various  proteids, 
the  student  is  referred  to  the  more  comprehensive  works  on  the 
analysis  of  foods  and  to  the  original  literature. 

Preparation  of  the  Sample 

Grind  the  material  in  a  coffee  or  spice  mill  until  the  powder  will 
pass  through  a  sieve  with  circular  holes  I  mm.  in  diameter. 

Dry  Matter 

Procedure. — Weigh  two  samples  of  the  substance  of  about 
5  grams  each  into  weighed  cover-glasses  which  are  provided 
with  covers  and  spring  clips  as  shown  in  Fig.  4,  page  8.  Heat 
for  five  hours  in  the  water  oven,  place  the  covers  on  the  cover- 
glasses,  and  weigh.  Heat  again  for  periods  of  one  hour  until  the 
weight  is  constant  to  2  mgms.  From  the  loss  of  weight  calcu- 
late the  percentage  of  dry  matter.  Save  the  residue  for  the 
determination  of  the  ether-soluble  matter. 


122 


QUANTITATIVE  ANALYSIS 


OUTLINE   FOR  THE  ANALYSIS  OF   FEEDING   MATERIALS. 

Determination  of  Dry  Matter,  Ash,  Proteids,  Ether  Extract,  Reducing  Sugars, 
Sucrose  (Dextrin  -f  Soluble  Starch),  Starch,  and  Crude  Fiber. 

Determine  proteids  and  ash  in  separate  portions  of  the  substance.  The  moisture, 
ether  extract,  and  carbohydrates  are  determined  as  follows : 

Weigh  out  sample,  dry  at  1 10°,  reweigh.     Calculate  dry  matter. 

RESIDUE  A 
Extract  with  dry  ether. 


RESIDUE  B 
Extract  with  boiling  alcohol. 


Ethereal  solution  (a)  contains  fats,  oils,  and  various  other 
substances.     Evaporate  the  ether  and  weigh  the  crude  fat. 


Alcoholic  solution  (£)  contains  sucrose  and  reducing  sugars. 
Evaporate  alcohol,  make  to  known  volume  with  water, 
remove  two  aliquot  parts  (i)  and  (2). 


Solution  (i) 
Determine  reducing 
sugars    by    Allihn's 
method. 


RESIDUE  C 
Digest  with  cold  water. 


Solution  (2) 

Invert  by  heating  with  acid.  Determine  re- 
ducing sugars  by  Allihn's  method.  Subtract 
reducing  sugars  found  in  (i).  Calculate 
sucrose  present. 


Filter. 


I 
Solution  (c}  contains  dextrin  and  soluble  starch.    Hydrolyze 

by  boiling   with    HC1.      Determine    dextrose   by   Allihn's 
method.     Calculate  dextrin  plus  soluble  starch. 
RESIDUE  D 

Boil  with  water  to  gelatinize  starch.     Convert  starch  to 

dextrin  and  maltose  by  means  of  malt  extract.     Filter. 


RESIDUE  E 
Boil  with  dilute  H2SO4.     Filter. 


Solution  (</)  contains  maltose  and  dextrin.  Hydrolyze  by 
boiling  with  HC1.  Determine  dextrose  in  aliquot  part  by 
Allihn's  method.  Calculate  the  starch  present. 


RESIDUE  F 
Boil  with  dilute  NaOH  solution. 


Solution  (<?)  discard. 


Filter. 


RESIDUE  G 

Filter  on  a  Gooch.     Weigh.     Ignite  and 
reweigh.     Loss  is  weight  of  crude  fiber. 


Solution  (/)  discard. 


AGRICULTURAL  ANALYSIS  123 

Ether  Extract 

Procedure. — Obtain  two  large  and  two  small  extraction  tubes  and 
fasten  hardened  fat-free  filter  paper  securely  over  one  end  of  the 
large  tubes  by  means  of  tinned  iron  wire.  Provide  the  small 
extraction  tube  with  a  double  layer  of  filter  paper,  using  ordinary 
quantitative  filter  paper  for  the  inside  layer  and  hardened  paper 
outside.  Place  the  residues  from  the  determination  of  dry  matter 
into  the  small  extraction  tubes,  place  these  inside  the  large  tubes, 
and  introduce  into  a  Soxhlet  extractor.  Pour  50  c.c.  of  dry  ether 
into  each  of  two  weighed  flasks  of  125  c.c.  capacity,  attach  the 
flasks  to  the  extraction  apparatus  as  in  the  determination  of  milk 
fat  by  the  Adams  method,  and  extract  for  sixteen  hours.  Remove 
the  ether  by  distillation  and  dry  the  flasks  and  contents  to  constant 
weight  in  the  water  oven.  Calculate  the  percentage  of  ether- 
soluble  matter  in  the  substance. 

Notes.  —  i.  The  term  ether  extract  is  used  for  the  constituents  of 
the  food  which  are  soluble  in  ether.  Besides  fats  and  oils  the  ether 
extract  may  contain  waxes,  resins,  chlorophyl,  coloring  matters,  and 
in  some  cases  bodies  containing  nitrogen  and  phosphorus. 

2.  Care  should  be  taken  not  to  extract  the  material  for  too  long 
a  period,  as  there  is  danger  of  the  oxidation  of  the  fats  and  oils. 
For  the  same  reasons  the  flasks  should  not  be  allowed  to  stand 
in  the  water  oven  for  an  unnecessary  length  of  time.  If  pos- 
sible, they  should  be  heated  to  constant  weight  in  an  atmosphere 
of  hydrogen. 

Separation  of  Carbohydrates 

By  Stone's  Method 

Procedure.  —  Use  the  residue  left  from  the  determination  of  the 
ether-soluble  matter.  Connect  the  Soxhlet  extractor  with  a  250  c.c. 
Erlenmeyer  flask  which  contains  150  c.c.  of  95  per  cent  alcohol 
and  extract  for  three  or  four  hours.  Evaporate  the  alcoholic 
extract  nearly  to  dryness,  add  water,  transfer  to  a  100  c.c.  gradu- 
ated flask,  and  fill  to  the  mark.  Use  this  solution  for  the  determi- 
nation of  reducing  sugars  and  sucrose,  filtering  if  necessary. 

Note.  —  Besides  the  sugars  hot  alcohol  dissolves  certain  waxes. 
On  evaporation  of  the  alcohol  and  the  addition  of  water  to  the 
extract,  these  are  precipitated. 


124  QUANTITATIVE  ANALYSIS 

Reducing  Sugars 
By  Allihn's  Method 

Principle. — This  determination  is  based  upon  the  same  chemical 
facts  as  the  determination  of  lactose ;  the  concentrations  of  the 
solutions  and  other  details  are  slightly  different. 

Procedure.  —  Place  30  c.c.  of  the  copper  sulphate  solution  and 
30  c.c.  of  Allihn's  alkaline  tartrate  solution  into  a  casserole,  add 
60  c.c.  of  water,  and  beat  to  boiling.  Add  25  c.c.  of  the  filtered 
solution  containing  the  sugars,  and  boil  for  two  minutes.  Filter 
immediately  without  diluting,  and  wash  with  hot  water  until  the 
filtrate  no  longer  gives  an  alkaline  reaction.  Dry  the  precipitate, 
ignite,  and  weigh  as  cupric  oxide.  Calculate  the  amount  of  copper 
in  the  precipitate  and  consult  Allihn's  table  on  page  207  to  find 
the  amount  of  dextrose  equivalent  to  this  amount  of  copper.  The 
percentage  of  reducing  sugars  in  the  sample  is  expressed  as  dex- 
trose. 

Notes.  —  I.  The  nitrate  should  be  examined  carefully  for  cu- 
prous oxide,  as  the  precipitate  has  a  tendency  to  run  through  the 
filter. 

2.  In  this  determination,  as  in  the  determination  of  lactose,  the 
conditions  prescribed  should  be  closely  observed.  The  solution 
analyzed  should  not  contain  more  than  one  per  cent  of  reducing 
sugars. 

Sucrose 

By  Clergef  s  Inversion  Method 

Principle.  —  By  heating  in  the  presence  of  an  acid,  sucrose  is 
hydrolyzed  and  forms  a  mixture  of  equal  amounts  of  dextrose  and 
levulose. 

Sucrose  Dextrose  Levulose 

C12H22Ou  4-  H20  =  C6H1206  +  C6H1206. 

The  reducing  sugars  thus  formed  can  be  determined  by  Allihn's 
method  and  the  amount  of  sucrose  calculated. 

Procedure.  —  Place  50  c.c.  of  the  solution  containing  the  reduc- 
ing sugars  and  sucrose  into  a  flask  marked  at  50  and  55  c.c.  Fill 
to  the  upper  mark  with  pure  concentrated  hydrochloric  acid  (sp. 
gr.  i. 20)  and  mix  well.  Place  in  water  and  heat  until  a  thermom- 


AGRICULTURAL  ANALYSIS 


125 


eter  held  with  the  bulb  near  the  center  of  the  sugar  solution 
reads  68°,  consuming  about  15  minutes  in  raising  it  to  this  tem- 
perature. Remove  the  flask  from  the  bath,  cool,  and  determine  by 
Allihn's  method  the  reducing  sugars  in  25  c.c.  of  the  solution 
which  have  been  made  neutral  by  the  addition  of  solid  sodium 
carbonate.  Calculate  the  amount  of  reducing  sugars  in  the  sub- 
stance. This  gives  the  reducing  sugars  formed  by  the  inversion 
of  the  sucrose,  plus  the  reducing  sugars  originally  present.  Sub- 
tract the  amount  of  reducing  sugar  in  the  original  sample  and 
calculate  the  weight  and  percentage  of  sucrose  present  The 
reducing  sugars  should  always  be  calculated  as  dextrose. 

Notes. —  i.    In  the  above  process  the  hydrochloric  acid  acts  as  a 
catalyzer,  accelerating  the  rate  at  which  the  sucrose  is  inverted. 

2.  The  details  of  the  Clerget  method  of 
inversion  should  be  observed  closely.  If  the  jl 

length  of  time  of  heating  is  too  short,  the  in- 
version will  be  incomplete.     If  the  heating  is        , 
prolonged    or    the   temperature    of    68°    ex- 
ceeded, some   of   the    levulose   will    be   de- 
composed. 

Dextrin  and  Soluble  Starch 

Principle.  —  These  substances  are  hydro- 
lyzed  by  heating  with  an  acid,  forming  dex- 
trose. The  dextrose  is  estimated  in  the 
usual  way,  and  the  sum  of  the  dextrin  plus 
soluble  starch  calculated. 

Procedure.  —  Place  the  residue  from  the  al- 
coholic extraction  into  a  beaker,  add  100  c.c. 
of  water,  and  allow  to  stand  from  eighteen  to 
twenty-four  hours  with  frequent  agitations. 
Filter  on  a  washed  linen  filter  which  is  placed 
on  a  Buchner  funnel  arranged  for  filtering 
with  the  aid  of  suction,  wash  the  residue  with 
cold  water  and  evaporate  on  the  steam  bath 
until  the  volume  of  the  solution  is  about  60 


V 


FIG.  30 


c.c.  Boil  the  solution  gently  for  two  hours  with  one  tenth  its 
volume  of  hydrochloric  acid  (sp.  gr.  1.125),  using  a  reflux  Hopkins 
condenser  as  illustrated  in  Fig.  30.  Cool  the  solution,  neutralize 


126  QUANTITATIVE  ANALYSIS 

with  solid  sodium  carbonate,  make  up  to  100  c.c.,  and  determine 
the  dextrose  in  25  c.c.  by  Allihn's  method.  From  the  amount  of 
dextrose  calculate  the  percentage  of  dextrin  plus  soluble  starch  in 
the  substance. 

Note.  —  Starch  which  is  dissolved  by  water  is  called  soluble 
starch.  It  gives  the  characteristic  blue  color  with  iodine  in  dis- 
tinction from  some  of  the  other  products  formed  from  starch,  like 
dextrin,  which  does  not  give  the  blue  color  when  tested  with 
iodine.  If  the  material  which  is  being  analyzed  has  been  sub- 
jected to  heat  or  friction,  as  in  the  grinding  of  corn  or  flour,  or  to 
the  action  of  acids,  then  a  portion  of  the  starch  may  have  been 
changed  to  the  soluble  form  and  will  be  found  in  the  aqueous 
extract  with  the  dextrin. 

Starch 

Diastase  Method 

Principle.  —  Starch  may  be  completely  separated  from  the  other 
insoluble  carbohydrates  by  the  action  of  diastase,  which  converts  it 
to  maltose  and  dextrin  and  has  no  action  on  the  other  insoluble 
carbohydrates,  which  can  be  removed  by  filtration.  By  hydrolyzing 
with  an  acid  the  maltose  and  dextrin  are  then  converted  to  dextrose. 


Maltose 


Dextrin 


=  2  C6H12Og. 


=  C6H1206. 


From  the  amount  of  dextrose  formed  the  starch  present  can  be 
calculated. 

Procedure.  —  Wash  the  residue  from  the  alcoholic  extraction  in 
the  above  determination  into  a  250  c.c.  flask  with  hot  water,  immerse 
the  flask  in  boiling  water,  and  stir  the  contents  until  the  starch  gel- 
atinizes. This  usually  takes  about  thirty  minutes.  Cool  to  55°  C, 
add  30  to  40  c.c.  of  malt  extract,  measured  accurately,  and  main- 
tain at  5  5  °  until  the  solution  no  longer  gives  the  starch  reaction 
when  tested  with  iodine  solution.  Two  or  three  hours  should  be 
sufficient  for  this  purpose.  The  detection  of  small  quantities  of 
starch  is  best  accomplished  by  adding  a  few  drops  of  iodine  to  a 
small  quantity  of  a  solution  on  a  glass  and  examining  it  by  means 


AGRICULTURAL  ANALYSIS  127 

of  a  microscope.  The  blue  color  if  present  can  be  seen  distinctly. 
Heat  the  solution  to  boiling,  filter  through  a  linen  filter,  and  wash 
the  residue  thoroughly  with  hot  water.  Make  the  filtrate  up  to  200 
c.c.,  add  20  c.c.  of  hydrochloric  acid  (sp.  gr.  1.125),  connect  with 
a  reflux  Hopkins  condenser,  and  heat  in  a  boiling  water  bath  for 
two  and  one  half  hours.  Nearly  neutralize  while  hot  with  solid 
sodium  carbonate  and  make  up  to  500  c.c.  Mix  the  solution  well, 
pour  through  a  dry  filter,  discarding  the  first  10  c.c.,  and  determine 
the  dextrose  in  25  c.c.  of  the  filtrate  by  Allihn's  method.  Correct 
for  the  copper  reducing  power  of  the  malt  extract.  Calculate  the 
percentage  of  starch  present. 

Preparation  of  Malt  Extract.  —  Pulverize  about  20  grams  of  malt 
and  allow  it  to  stand  for  several  hours  with  100  c.c.  of  water.  Shake 
the  solution  occasionally.  Filter  and  add  to  the  solution  two  or 
three  drops  of  chloroform  to  prevent  the  growth  of  fungi.  Deter- 
mine the  amount  of  soluble  carbohydrates  in  the  malt  extract  by 
proceeding  as  follows :  take  an  amount  of  the  solution  equal  to 
that  used  in  the  determination  of  starch,  dilute  to  200  c.c.,  hydrolyze 
by  heating  with  hydrochloric  acid,  and  determine  the  amount  of 
dextrose  in  25  c.c.  by  Allihn's  method.  In  determining  starch, 
make  the  proper  correction  for  the  cuprous  oxide  reduced  by  the 
malt  extract. 

Notes.  —  i.  When  barley  is  exposed  to  moist  warm  air,  the  grains 
sprout.  The  starch  present  is  converted  to  dextrin  and  dextrose, 
and  a  ferment  known  as  diastase  is  formed.  Diastase  has  the 
power  of  converting  starch  into  dextrin  and  maltose,  the  latter  being 
the  chief  product  when  the  temperature  is  kept  at  50-60°.  At 
higher  temperatures  there  is  a  larger  yield  of  dextrin.  The  diastase 
is  soluble  in  water  and  consequently  may  be  extracted  from  the 
malt  and  preserved  in  aqueous  solution. 

2.  As  all  starches  are  not  affected  in  the  same  manner  or  to  the 
same  degree  by  the  action  of  diastase,  it  may  be  necessary  in  some 
cases  to  subject  the  material  to  the  action  of  the  diastase  for  a 
longer  time. 

Saliva  Method 

Principle.  —  Saliva  contains  the  ferment  ptyalin,  which  possesses 
the  power  of  bringing  starch  into  solution  by  converting  it  first  into 
dextrin  and  finally  into  maltose.  Eventually  dextrose  is  formed. 

Procedure.  —  Collect  about  30  c.c.  of  saliva  by  chewing  a  piece 


128  QUANTITATIVE  ANALYSIS 

of  pure  paraffin.  Filter  and  make  exactly  neutral  to  litmus  paper 
by  adding  a  0.2  per  cent  hydrochloric  acid  solution  drop  by  drop. 
Bring  the  gelatinized  starch  solution,  obtained  as  in  the  determina- 
tion of  starch  by  the  diastase  method,  to  40°.  Add  about  15  c.c. 
of  the  saliva  and  allow  the  solution  to  remain  at  40°  until  a  drop  of 
the  liquid  gives  no  test  for  starch  with  the  iodine  solution.  Filter 
the  solution  on  a  washed  linen  filter,  make  up  to  200  c.c.,  hydrolyze 
with  acid,  and  proceed  as  in  the  determination  of  starch  by  the 
diastase  method. 

Notes.  —  i.  The  above  method  for  the  determination  of  starch 
may  be  advantageously  employed  when  only  a  few  determinations 
are  to  be  made.  Saliva  has  the  advantage  over  the  malt  extract  in 
that  it  contains  no  soluble  carbohydrates  and  consequently  requires 
no  blank  determination. 

2.  The  action  of  normally  alkaline  saliva  is  increased  by  neu- 
tralization.    An  excess  of  acid  must  be  avoided,  since  as  small  an 
amount  as  0.003  per  cent  of  hydrochloric  acid  not  only  greatly 
checks  the  action  of  the  ferment,  but  also  tends  to  destroy  it.     The 
most  favorable  temperature  for  the  action  of  the  ptyalin  is  40°. 

3.  Starch  is  sometimes  determined  by  heating  the  residue  from 
the  aqueous  extraction  with  dilute  hydrochloric  acid,  and  estimat- 
ing the  dextrose  formed.     By  this  method  the  pentosans  and  cer- 
tain other  carbohydrates  are  also  converted  to  reducing  sugars 
and  consequently  are  calculated  as  starch.     If  the  other  insoluble 
carbohydrates  are  absent,  the  method  gives  satisfactory  results. 

Crude  Fiber 

Principle.  —  Upon  boiling  the  residue  from  the  starch  determina- 
tion with  dilute  acid,  the  pentosans  and  gums  are  changed  to  solu- 
ble reducing  sugars  and  certain  nitrogenous  bodies  are  dissolved. 
Hot  dilute  sodium  hydroxide  solution  removes  other  albuminous 
matter  and  products  of  decomposition.  The  residue  is  crude  fiber. 

Procedure.  —  Crude  fiber  may  be  determined  in  the  residue  from 
the  determination  of  starch,  or  in  case  the  carbohydrates  were  not 
separated,  in  the  residue  from  the  determination  of  ether-soluble 
matter.  Wash  the  residue  into  a  500  c.c.  flask  with  hot  1.25  per 
cent  sulphuric  acid.  Add  enough  of  the  acid  to  bring  the  volume 
of  the  solution  to  200  c.c.,  connect  the  flask  with  a  Hopkins  con- 
denser, boil  at  once,  and  continue  the  boiling  for  thirty  minutes. 


AGRICULTURAL  ANALYSIS  129 

Filter  through  a  linen  filter  and  wash  with  boiling  water  until  the 
washings  are  no  longer  acid.  Rinse  the  substance  back  into  the 
same  flask  with  200  c.c.  of  boiling  1.25  per  cent  solution  of  sodium 
hydroxide,  which  should  be  as  free  as  possible  from  sodium  car- 
bonate. Boil  at  once  and  continue  the  boiling  for  thirty  minutes. 
Filter  on  a  Gooch  filter  which  has  been  prepared  with  a  thin  layer 
of  asbestos  and  wash  with  boiling  water  until  the  washings  are 
neutral.  Dry  at  1 10°,  weigh,  incinerate  completely,  and  reweigh. 
The  loss  of  weight  is  crude  fiber. 

Notes.  —  i.  Crude  fiber  is  not  in  any  sense  a  chemical  compound, 
but  is  a  mixture  and  includes  the  substances  which  make  up  the 
framework  of  vegetable  compounds.  It  consists  for  the  greater 
part  of  cellulose,  together  with  lignin,  pentosans,  and  a  certain 
amount  of  proteid  matter. 

2.  Instead  of  using  a  Gooch  crucible,  the  crude  fiber  can  be 
filtered  on  a  tared  filter,  washed  free  from  alkali,  dried  at  110°, 
weighed,  ignited,  and  reweighed.  The  loss  of  weight  gives  the 
crude  fiber  plus  the  filter.  A  blank  should  be  run  with  another 
filter  to  show  the  loss  caused  by  treatment  with  alkali,  and  the 
proper  correction  made. 

Total  Proteids 

Procedure.  —  Weigh  from  I  to  2  grams  of  the  substance  into 
a  Kjeldahl  flask,  add  0.65  gram  of  mercury,  25  c.c.  of  pure  con- 
centrated sulphuric  acid,  and  digest  until  the  solution  is  colorless 
or  of  a  light  straw  color.  Dilute  with  nitrogen-free  water  and 
determine  the  nitrogen  present  by  distillation  as  in  the  determina- 
tion of  proteids  in  milk.  Calculate  the  percentage  of  proteids 
present  in  the  sample. 

Note.  —  For  some  of  the  more  common  cereals  the  factors  for 
the  conversion  of  the  nitrogen  to  proteids  are : 

Wheat,     5.70  Rye,      5.62 

Oats,        6.31  Corn,    6.39 

Barley,     5.82 

The  factor  6.25  should  be  used  when  other  factors  are  not  given. 

Ash 

Procedure.  —  Weigh  from  2  to  3  grams  of  the  substance  into 
a  porcelain  crucible,  char  in  the  ash  muffle,  then  burn  to 


130  QUANTITATIVE  ANALYSIS 

whiteness  at  the  lowest  possible  red  heat.  If  a  white  ash  can- 
not be  obtained  in  this  manner,  extract  the  charred  mass  with 
water,  collect  the  insoluble  residue  on  a  filter,  burn,  add  this  ash 
to  the  residue  from  the  evaporation  of  the  aqueous  extract,  and 
heat  at  a  low  redness  until  white.  Calculate  the  percentage  of 
ash  in  the  sample. 

REFERENCES 

LEACH,   Food  Inspection  and  Analysis,  Chapter  IX,  p.  213. 
SHERMAN,  Jour.  Am.  Chem.  Soc.,  19,  291  (1897). 
STONE,  Jour.  Am.  Chem.  Soc.,  19,  193  (1897). 


THE   ANALYSIS    OF  FERTILIZERS 

Fertilizers  are  those  materials  which  are  added  to  soils  to  supply 
supposed  deficiencies  in  plant  foods,  or  to  render  more  available 
the  stores  already  present  (Wiley). 

The  most  important  elements  present  in  fertilizers  and  those 
most  often  estimated  are  nitrogen,  potassium,  and  phosphorus. 
These  elements  are  used  directly  as  plant  food  and  are  conse- 
quently of  great  commercial  importance.  Certain  substances, 
however,  may  be  used  as  fertilizers  which  in  themselves  are  of 
only  small  value  as  plant  food.  Lime,  for  example,  has  great 
value  as  a  fertilizer  entirely  independent  of  the  fact  that  growing 
plants  require  some  calcium  as  a  food.  It  causes  chemical 
changes  in  the  soil,  rendering  certain  of  the  constituents  available 
to  the  plant.  For  example,  feldspar  and  certain  other  rocks  con- 
tain potassium  in  a  form  which  is  inaccessible  to  the  plant.  The 
lime  acts  chemically  on  these  rocks,  changing  the  potassium  to  a 
form  in  which  it  can  be  used.  Besides  the  nitrogen,  potassium, 
and  phosphorus,  then,  there  are  often  present  in  fertilizers  certain 
substances  which  have  an  indirect  value,  and  which  are  of  great 
scientific  and  often  of  .great  commercial  interest.  The  analyst  is, 
therefore,  often  called  upon  to  estimate  organic  and  volatile  mat- 
ter, Na,  Ca,  Mg,  Fe,  Al,  Mn,  Si,  S,  Cl,  Fl. 

It  is  of  great  importance  to  the  analyst  to  know  the  origin  of 
the  fertilizer,  as  the  methods  for  the  determination  of  an  element 
differ  with  the  state  of  chemical  combination  in  which  the  element 
is  present.  For  example,  in  determining  the  nitrogen  in  such  sub- 
stances as  leather  scraps,  ammonium  sulphate,  and  sodium  nitrate, 
quite  different  procedures  are  followed. 


AGRICULTURAL  ANALYSIS 


Fertilizers  are  obtained  either  from  natural  sources  or  from 
waste  materials.  They  are  used  in  the  raw  state  and  also  after 
being  subjected  to  various  forms  of  treatment  to  render  their  con- 
stituents more  available.  They  are  often  mixed  with  other  sub- 
stances in  order  to  furnish  a  product  which  contains  all  three  of 
the  essential  elements,  nitrogen,  potassium,  and  phosphorus. 
These  are  known  as  mixed  fertilizers.  The  natural  fertilizers  are 
deposits  of  plant  food  which  have  been  brought  together  during 
the  various  geological  epochs  through  which  the  earth  has  passed ; 
some  of  these  deposits  are  the  Stassfurt  salts,  rock  phosphates, 
and  Chili  saltpeter.  The  waste  materials  from  factories,  slaughter- 
houses, blast  furnaces,  etc.,  have  come  into  general  use.  Some  of 
the  most  important  of  these  are  blast  furnace  slag,  dried  blood, 
manure,  sewage,  bones,  horns,  hoofs,  and  a  great  deal  of  organic 
refuse.  The  following  table  gives  the  composition  of  some  of  the 
fertilizers  which  are  in  general  use. 

THE  COMPOSITION  OF  TYPICAL  FERTILIZERS 


NITROGEN 

PHOSPHORUS 

POTASSIUM 

Citrate- 
soluble 

Total 

Dried  Blood 

14.10 
6.70 
20.50 

2-35 

4-34 
2.60 
2.64 

1.70 
i-57 

2.38 

5.20 

0.30 

0.75 

9-55 
7.48 
12.48 
12.97 
6.58 
5-3i 
5-37 

6.80 
4-20 
II.OI 

2-35 
6.89 

Tankapje 

Ammonium  Sulphate     .... 
Tobacco  Stems    
"Wood  Ashes  

2.83 

5-94 
5-03 
0.72 

6-37 
4.26 

4-33 

Kainit    

Raw  Bone  Meal  .          .... 

Acidulated  Bone  . 

Steamed  Bone 

Raw  Phosphate  Rock    .... 
Acid  Phosphate  Rock  .... 
"  Corn  and  Wheat  Grower"  .     . 
"  Onion,  Potato,  and  Tobacco  "  . 

Sampling 

Obtain  a  representative  sample  from  the  total  amount  of  ferti- 
lizer, mix  it  thoroughly,  grind  finely  if  necessary,  and  pass  the 
sample  for  analysis  through  a  sieve  having  circular  openings  I 
mm.  in  diameter.  Mix  thoroughly  and  transfer  about  30  grams 
of  the  sample  to  a  weighing  tube.  For  special  methods  for  sam- 
pling manures,  etc.,  see  Wiley's  Agricultural  Analysis^  Vol.  II. 


132  QUANTITATIVE  ANALYSIS 

Dry  Matter 

Procedure. — For  potassium  salts,  sodium  nitrate,  or  ammonium 
sulphate,  weigh  out  2-3  grams  upon  a  cover-glass  and  heat  in  the 
air  bath  at  130°  for  one  hour.  Remove  from  the  bath,  cool,  and 
weigh.  Heat  again  for  thirty  minutes.  Cool  and  weigh.  Re- 
peat until  a  constant  weight  is  obtained.  For  all  other  ferti- 
lizers heat  the  sample  for  five  hours  at  100°  in  the  water  oven. 
For  this  determination  it  is  best  to  use  cover-glasses  with  ground 
edges  and  provided  with  a  clip.  From  the  weight  of  the  residue 
calculate  the  percentage  of  dry  matter. 

Note.  —  In  the  analysis  of  many  fertilizers  the  determination  of 
hygroscopic  water  is  a  matter  of  extreme  difficulty,  owing  to  the 
decomposition  of  the  fertilizer  by  heat.  Hence,  the  loss  in  weight 
on  heating  may  be  due  not  only  to  hygroscopic  water,  but  also  to 
chemically  combined  water,  organic  matter,  ammonia,  etc. 


PHOSPHORUS 

Phosphorus  is  found  in  fertilizers  in  a  state  of  organic  combina- 
tion, as  in  tankage,  oil  cake,  and  other  organic  materials ;  and  in 
phosphoric  acid,  either  in  the  free  state  or  combined  with  certain 
bases,  as  in  superphosphates  and  steamed  bone.  In  general,  the 
methods  for  the  determination  of  phosphorus  are  the  same  in  both 
cases ;  the  methods  of  destroying  the  organic  matter,  however, 
may  differ  considerably. 

Phosphoric  acid  is  present  in  fertilizers  in  several  different 
states  of  combination,  which  will  be  more  easily  understood  if  the 
method  of  manufacturing  these  fertilizers  is  considered  briefly. 
Finely  ground  rock  phosphate,  Ca3(PO4)2,  is  treated  with  sulphu- 
ric acid  in  lead  tanks,  the  object  usually  being  to  produce  the  soluble 
monocalcium  phosphate.  The  nature  of  the  product  obtained, 
however,  varies  with  certain  factors,  such  as  the  purity  of  the  rock 
phosphate,  the  quantity  of  sulphuric  acid  used,  and  the  tempera- 
ture at  which  the  reaction  takes  place.  The  changes  may  be 
represented  by  the  following  equations  : 

(dicalcium  phosphate) 

+  H2S04  =  Ca2H2(P04)2  +  CaSO4. 


AGRICULTURAL  ANALYSIS  133 

(monocalcium  phosphate) 

Ca3(P04)2  +  2  H2S04=  CaH4(P04)2  +  2  CaSO4. 

(ortho-phosphoric  acid) 

Ca3(P04)2  +  3  H2S04  =  2  H3P04  +  3  CaSO4. 

Monocalcium  phosphate  on  standing  in  contact  with  tricalcium 
phosphate  undergoes  a  change,  or  reversion,  which  may  be  shown 
by  the  following  equation : 

CaH4(P04)2  +  Ca3(P04)2  =  2  Ca2H2(PO4)2. 

The  dicalcium  phosphate  formed  in  this  way  is  known  as 
"  reverted  phosphate." 

The  phosphates  in  fertilizers  may  be  classified  according  to 
their  solubilities  : 

[Soluble  in  cold  water.  [Free  phosphoric  acid, 
i.  J  Readily  available  f  or  J  Monocalcium  phosphate, 
plants.  Monomagnesium  phosphate. 


2. 


Soluble  in  weak  acids  and 
in  solutions  of  certain  salts 
(ammonium  citrate)  called 
the  citrate-soluble. 
Readily  available  for 
plants. 


Dicalcium  phosphate. 


[Soluble     in    strong     acidsl  Tricalcium  phosphate, 
-   I  only.  I  also  phosphates  of  aluminium  and 

[Slowly  available  for  plants.)  iron. 

Total  Phosphorus 

Principle.  —  The  organic  matter  present  is  oxidized  by  means  of 
aqua  regia,  the  phosphorus  remaining  in  solution  as  phosphoric 
acid.  This  is  separated  from  the  bases  present  by  precipitating 
with  ammonium  molybdate  solution,  as  the  ammonium  phospho- 
molybdate.  The  ammonium  phosphomolybdate  is  dissolved  in 
ammonium  hydroxide  and  the  phosphorus  precipitated  as  magne- 
sium ammonium  phosphate. 


134  QUANTITATIVE  ANALYSIS 

Procedure.  —  Weigh  2-3  grams  of  the  sample  into  a  No.  4 
beaker  and  add  to  it  25  c.c.  of  strong  hydrochloric  acid  (sp.gr. 
i. 20)  and  10  c.c.  of  strong  nitric  acid  (sp.  gr.  1.40).  Cover  the 
beaker  with  a  glass  and  heat  gently  until  all  the  organic  matter  is 
destroyed.  Repeat  the  treatment  with  aqua  regia  if  necessary. 
Cool  the  solution,  dilute  it  to  exactly  250  c.c.,  mix  thoroughly,  and 
filter  through  a  dry  filter,  discarding  the  first  10  c.c.  of  the  filtrate. 
Remove  exactly  50  c.c.  of  the  filtrate  with  a  pipette,  neutralize 
carefully  with  ammonium  hydroxide,  and  add  a  few  drops  of  nitric 
acid  to  dissolve  any  precipitate  which  may  have  been  formed. 
Dissolve  15  grams  of  pure  ammonium  nitrate  in  25  c.c.  of  warm 
water,  and  add  it  to  the  solution.  To  the  warm  solution  add  75 
c.c.  of  the  ammonium  molybdate  solution  and  digest  at  about  65° 
for  an  hour.  Filter  and  wash  the  precipitate  with  a  solution  of 
ammonium  nitrate  (100  grams  per  liter)  until  5  c.c.  of  the  wash 
water  give  no  test  for  chlorides.  The  yellow  precipitate  need 
not  be  completely  removed  from  the  beaker.  Test  the  filtrate  for 
complete  precipitation  by  the- addition  of  10  c.c.  of  the  molybdate 
solution  and  renewed  digestion.  A  white  precipitate  may  be 
disregarded. 

Molybdic  acid  is  an  expensive  reagent ;  consequently  all  resi- 
dues from  this  determination  should  be  placed  in  a  bottle  provided 
for  them. 

Dissolve  the  yellow  precipitate  by  pouring  a  solution  containing 
equal  parts  of  ammonium  hydroxide  and  hot  water  through  the 
filter,  receiving  the  solution  in  the  beaker  in  which  the  first  precip- 
itation took  place.  Wash  the  filter  several  times  with  hot  water 
and  ammonium  hydroxide.  Do  not  allow  the  total  volume  of  the 
filtrate  to  amount  to  more  than  100  c.c.  Nearly  neutralize  the 
solution  with  dilute  hydrochloric  acid,  then  cool  and  add  mag- 
nesia mixture  (10  c.c.)  from  a  burette,  letting  it  run  in  at  the  rate 
of  one  drop  per  second,  and  stirring  the  solution  vigorously  at 
the  same  time.  After  fifteen  minutes  add  30  c.c.  of  ammonium 
hydroxide  (sp.  gr.  0.96)  and  allow  to  stand  for  several  hours. 
Filter  and  treat  the  precipitate  as  in  the  determination  of  mag- 
nesium, Exercise  VII.  From  the  weight  of  the  magnesium  pyro- 
phosphate  calculate  the  weight  of  phosphoric  anhydride  and  the 
percentage  of  the  latter  in  the  sample  taken.  Calculate  the  per- 
centage of  phosphorus. 


AGRICULTURAL  ANALYSIS  135 

Notes.  —  i.  Organic  matter  in  a  fertilizer  may  also  be  destroyed 
and  the  phosphorus  brought  into  solution  by  any  of  the  follow- 
ing methods  : 

a.  Ignition  and  solution  of  residue  in  hydrochloric  acid. 

b.  Digestion  with  concentrated  sulphuric    acid   and  potassium 
nitrate. 

c.  Evaporation  with  concentrated  magnesium    nitrate  solution, 
ignition,  and  solution  of  the  residue  in  hydrochloric  acid* 

2.  The    residue    left    from    the    treatment    with  aqua    regia 
generally   consists    of    insoluble    mineral    matter    such    as    silica 
and    silicates,   these  substances   being    originally  present   in  the 
mineral  phosphate. 

3.  Under   certain   conditions   phosphorus  may  be    precipitated 
from  an  acid  solution  as  ammonium  phosphomolybdate,  separating 
it  from  any  bases  which  may  be  present  in  the  solution.     Arsenic 
and  silica,  however,  if  present,  must  be  removed,  as  they  precipi- 
tate from  the  solution  with  phosphorus. 

The  composition  of  ammonium  phosphomolybdate  is  not  con- 
stant, but  varies  with  the  conditions  under  which  it  is  precipitated. 
When  precipitated  under  the  above  conditions  and  dried  at  130°, 
the  precipitate  has  the  composition  (NH4)3PO4-  12  MoO3.  It  is 
usually  not  practicable  to  weigh  the  phosphorus  in  this  form, 
although  this  is  done  by  some  analysts.  It  is  more  satisfactory  to 
redissolve  the  precipitate  in  ammonium  hydroxide,  precipitate  the 
phosphorus  as  magnesium  ammonium  phosphate,  and  weigh  it  as 
magnesium  pyrophosphate. 

4.  The   following   conditions    should   be    observed  in  order  to 
obtain  the  complete  precipitation  of  phosphorus    as    ammonium 
phosphomolybdate  : 

Organic  matter  must  not  be  present. 

The  phosphorus  must  be  present  as  ortho-phosphoric  acid. 

The  precipitate  is  less  soluble  in  solutions  of  ammonium  nitrate 
and  ammonium  molybdate  than  in  water.  These  salts  should, 
therefore,  be  present  in  excess.  The  presence  of  ammonium 
nitrate,  moreover,  makes  the  precipitation  take  place  more  readily. 

The  solution  should  be  acid  with  nitric  acid,  but  with  only  a 
slight  excess,  as  the  precipitate  is  appreciably  soluble  in  concen- 
trated acids.  It  is  most  soluble  in  hydrochloric  acid,  less  soluble 
in  sulphuric  acid,  while  nitric  acid  exercises  the  least  solvent  action. 
The  precipitate  forms  much  more  readily  at  65°  than  at  the 


OF  THE 

UNIVERSITY 


136  QUANTITATIVE  ANALYSIS 

ordinary  temperature.  A  higher  temperature  is  attended  by  the 
precipitation  of  molybdic  anhydride  (  MoO3).  The  precipitation 
is  also  hastened  by  agitating  the  solution. 

5.  The  yellow  precipitate  is  dissolved  in  ammonium  hydroxide 
with  the  formation  of  ammonium  phosphate  and  ammonium  molyb- 
date. 

6.  Under  certain  conditions  the  precipitate  may  be  dissolved  in 
standard  alkali  according  to  the  equation 


(NH4)3PO4-i2  MoO3  +  23  NaOH  = 

ii  Na2MoO4-KNH4)2MoO4  +  NaNH4HPO4  +  ii  H2O 


and  the  excess  of  alkali  titrated  with  standard  nitric  acid.  This 
method  is  used  extensively  when  a  large  number  of  determinations 
must  be  made. 

7.  The  addition  of  a  large  excess  of  the  magnesia  mixture  should 
be  avoided,  as  it  tends  to  throw  down  magnesium  hydroxide  and 
may  also  cause  molybdic  anhydride  to  separate  with  the  precipitate. 
Molybdic  anhydride  may  also  separate  if  the  solution  is  too  con- 
centrated. 

Water-soluble  Phosphorus 

Procedure.  —  Place  about  two  grams  of  the  fertilizer  upon  a  9  cm. 
filter,  add  a  little  water  from  a  wash  bottle,  let  it  run  through  the 
filter,  add  more  water,  and  repeat  this  treatment  until  the  filtrate 
measures  about  225  c.c.  Be  sure  to  allow  each  portion  of  water  to 
pass  through  the  filter  before  more  is  added.  Save  the  washed 
residues  for  the  determination  of  the  citrate-insoluble  phosphorus. 
If  the  filtrate  is  turbid,  add  a  little  hydrochloric  acid.  Make 
the  filtrate  up  to  250  c.c.  and  mix  thoroughly.  Now  measure  out 
50  c.c.,  add  75  c.c.  of  ammonium  molybdate  solution,  and  proceed 
as  in  the  determination  of  total  phosphorus.  Save  the  remainder 
of  this  filtrate  for  the  determination  of  soluble  nitrogen. 

Citrate-insoluble   Phosphorus 

Procedure.  —  Heat  100  c.c.  of  strictly  neutral  ammonium  citrate 
solution  (sp.  gr.  1.09)  to  65°  C.  in  a  200  c.c.  Erlenmeyer  flask 
placed  in  a  bath  of  warm  water,  keeping  the  flask  loosely  stop- 
pered to  prevent  evaporation.  When  the  citrate  solution  in  the 
flask  has  reached  65°,  drop  into  it  the  filter  containing  the 


AGRICULTURAL  ANALYSIS  137 

washed  residue  from  the  water-soluble  phosphorus  determination, 
stopper  tightly  with  a  smooth  rubber  stopper,  and  shake  violently 
until  the  filter  paper  is  reduced  to  a  pulp.  Place  the  flask  back 
into  the  bath  and  maintain  the  water  in  the  bath  at  such  a  temper- 
ature that  the  contents  of  the  flask  will  stand  exactly  at  65°. 
Shake  the  flask  every  five  minutes.  At  the  end  of  exactly  thirty 
minutes  from  the  time  the  filter  and  residue  were  introduced,  re- 
move the  flask  from  the  bath  and  filter  as  quickly  as  possible 
upon  a  1 5  cm.  filter.  Use  a  filter  pump  and  support  the  filter  with 
a  cone  of  hardened  paper.  Wash  thoroughly  with  water  at  65° 
until  a  few  cubic  centimeters  of  the  filtrate  give  no  test  for  phos- 
phorus with  ammonium  molybdate  solution.  It  is  essential  that 
the  digestion  with  ammonium  citrate  takes  place  precisely  as  di- 
rected and  also,  that  at  the  end  of  the  half  hour's  digestion  the 
liquid  be  filtered  immediately.  Transfer  the  filter  and  contents  to 
a  small  porcelain  dish,  ignite  in  the  ash  muffle  until  all  organic 
matter  is  destroyed,  add  25  c.c.  of  concentrated  hydrochloric  acid 
and  10  c.c.  of  concentrated  nitric  acid,  and  digest  until  all  the 
phosphate  is  dissolved.  Dilute  the  solution  to  250  c.c.,  mix 
thoroughly,  and  filter  through  a  dry  filter.  Take  50  c.c.,  add  about 
15  grams  of  dry  ammonium  nitrate  and  75  c.c.  of  the  ammonium 
molybdate  solution,  and  proceed  as  in  the  determination  of  total 
phosphorus. 

Notes. —  i.  The  above  procedure  is  to  be  followed  in  the  analy- 
sis of  acidulated  samples.  For  non-acidulated  samples  treat  2 
grams  of  the  phosphate  material,  without  previous  washing  with 
water,  precisely  in  the  way  above  described,  except  that  in  case 
the  substance  contains  much  animal  matter  (bone,  fish,  etc.)  the 
residue  insoluble  in  ammonium  citrate  should  be  digested  in  a 
Kjeldahl  flask  with  concentrated  sulphuric  acid  and  potassium 
nitrate  until  the  organic  matter  is  destroyed. 

2.  The  determination  of  this  form  of  phosphorus  is  essentially 
conventional,  and  the  results  obtained  are  of  relative  value  only. 

Citrate-soluble  Phosphorus 

The  sum  of  the  water-soluble  and  citrate-insoluble  phosphorus 
subtracted  from  the  total  gives  the  citrate-soluble.  Express  the 
results  as  percentage  of  phosphoric  anhydride  and  also  as  per- 
centage of  phosphorus  in  the  sample. 


138  QUANTITATIVE  ANALYSIS 

NITROGEN 

Nitrogen  may  be  present  in  fertilizers  in  any  or  all  of  the  follow- 
ing forms:  (i)  in  animal  or  vegetable  substances,  in  which  it  is 
present  in  a  state  of  organic  combination — dried  blood,  cotton-seed 
meal,  etc.;  (2)  as  ammonia  or  its  combinations — ammonium 
sulphate ;  (3)  in  a  more  highly  oxidized  state  as  salts  of  nitrous 
or  nitric  acid — Chili  saltpeter. 

Total  Nitrogen  in  the  Absence  of  Nitrates 

In  case  no  nitrates  or  nitrites  are  present,  the  ordinary  Kjeldahl 
method  as  described  under  the  analysis  of  milk  may  be  employed, 
using  from  one  to  two  grams  of  the  sample  for  analysis.  Many 
mixed  commercial  fertilizers,  however,  contain  nitrates,  so  that  the 
process  must  be  modified  to  meet  this  condition. 

Total  Nitrogen  when  Nitrates  are  Present 

Principle.  — The  method  depends  on  the  reduction  of  the  nitrates 
to  ammonia,  the  digestion  with  sulphuric  acid  to  oxidize  any  or- 
ganic matter,  and  the  distillation  of  the  ammonia  in  the  usual  way. 

Procedure. — Introduce  from  I  to  2  grams  of  the  sample  into 
a  clean  Kjeldahl  flask,  being  careful  that  none  of  the  substance  re- 
mains on  the  neck.  Add  30  c.c.  of  concentrated  sulphuric  acid 
containing  2  grams  of  salicylic  acid,  then  add  gradually  2  grams 
of  zinc  dust,  shaking  the  contents  of  the  flask  at  the  same 
time.  Place  the  flask  on  the  digestion  stand  and  heat  over  a  low 
flame  until  all  danger  from  frothing  has  passed.  Increase  the 
heat  until  the  acid  boils  briskly  and  continue  the  boiling  until 
white  fumes  cease  to  come  off,  which  should  take  from  five  to  ten 
minutes.  Add  0.65  gram  metallic  mercury  and  continue  the  boil- 
ing until  the  liquid  in  the  flask  is  colorless  or  nearly  so.  In  case 
the  contents  of  the  flask  are  solid  before  the  digestion  is  complete, 
add  10  c.c.  of  sulphuric  acid.  Complete  the  oxidation  with  a  little 
potassium  permanganate  in  the  usual  way  and  proceed  with  the 
determination  as  described  in  the  directions  for  the  analysis  of 
milk.  In  case  more  than  25  c.c.  of  the  sulphuric  acid  were  used 
in  the  digestion,  the  amount  of  sodium  hydroxide  used  in  neutrali- 
zation should  be  increased  proportionally.  Calculate  the  percent- 
age of  nitrogen  in  the  fertilizer. 


AGRICULTURAL  ANALYSIS  139 

Notes.  —  I.  The  salicylic  acid  which  is  added  in  this  determina- 
tion facilitates  the  reduction  of  the  nitrate  by  forming  with  it  a 
nitrophenol,  a  compound  in  which  the  nitro  group  is  easily  reduced. 
The  change  may  be  represented  by  the  equation : 

(salicylic  acid) 

2  C6H4C°QH  +  2  NaN03  +  H2S04 

nitrophenol 

=  2  C6H4  °Q  +  Na2S04  +  2  C02  +  2  H2O. 

The  nitrophenol  thus  formed  is  then  reduced  by  hydrogen  formed 
by  the  action  of  sulphuric  acid  on  zinc  dust. 

amidophenol 

/"»     T  T       ^  -H        I      _    T  T  /""*     TLT      ^  *•*•          i       ~.   T  T     t~\ 


The  amidophenol  is  oxidized  by  digestion  with  sulphuric  acid,  the 
nitrogen  being  left  in  the  solution  in  the  form  of  ammonium 
sulphate. 

2CeH4NH  +27H2S04  =  (NH4)2S04  +  i2C02  +  3oH20  +  26S02. 

The  above  reactions  are  stated  to  make  more  apparent  the  func- 
tions of  the  various  reagents  in  the  change  of  the  nitrate  to 
ammonium  sulphate.  They  do  not  represent  all  the  chemical 
changes  which  take  place  during  this  process,  as  there  occur  many 
other  reactions  of  a  complex  nature. 

2.  Foaming  during  the  distillation  of  the  ammonia  may  be  pre- 
vented by  the  addition  of  a  small  piece  of  paraffin  to  the  contents 
of  the  Kjeldahl  flask. 

3.  A    blank    determination    should    be   carried    out   with    the 
reagents  used  in  this  analysis,  and  the  proper  corrections  made. 

Nitrogen  Soluble  in  Water 

Procedure.  —  Measure  50  c.c.  from  the  water  solution  prepared 
for  the  determination  of  soluble  phosphorus  and  determine  the 
nitrogen  present  by  the  modified  Kjeldahl  method  used  for  the 
determination  of  nitrogen  in  the  presence  of  nitrates. 


140  QUANTITATIVE  ANALYSIS 

Nitrogen  as  Ammonium  Salts 

Procedure. — Weigh  1.5  to  3  grams  of  the  substance  to  be  ana- 
lyzed into  a  500  c.c.  Kjeldahl  flask,  add  300  c.c.  of  nitrogen-free 
water,  and  about  5  grams  magnesium  oxide  free  from  carbonate. 
Distil  150-200  c.c.  of  the  liquid  into  a  flask  containing  a  measured 
volume  of  standard  acid.  Titrate  the  excess  of  acid  with  standard 
alkali  and  calculate  the  percentage  of  ammonia  and  nitrogen 
present. 

Note.  —  In  the  absence  of  organic  nitrogen  caustic  soda  may  be 
used  instead  of  magnesium  oxide.  The  use  of  caustic  soda  in  the 
presence  of  organic  nitrogen  is  prohibited  by  the  fact  that  it  de- 
composes the  organic  matter  with  the  formation  of  ammonia. 

POTASSIUM 

Potassium  may  be  found  in  fertilizers  in  organic  combination, 
as  in  tobacco  waste  and  cotton-seed  hulls,  and  in  inorganic 
salts,  as  carbonate  in  the  ash  obtained  from  burning  plants  of  all 
kinds,  or  as  chloride  or  sulphate  in  certain  mineral  deposits,  such 
as  the  Stassfurt  salts.  The  preliminary  treatments  of  the  various 
substances  containing  potassium  differ  considerably ;  however,  the 
final  method  of  precipitating  and  weighing  the  potassium  is  the 
same  in  all  cases.  For  the  determination  of  potassium  it  is  essen- 
tial that  all  organic  matter  be  destroyed,  and  that  the  potassium 
be  brought  into  a  soluble  form. 

Potassium  in  Mixed  Fertilizers 

Principle. — This  determination  is  based  upon  the  fact  that  po- 
tassium chlorplatinate  is  insoluble  in  strong  alcohol,  whereas  cer- 
tain other  elements  which  might  be  present,  such  as  sodium,  form 
easily  soluble  salts.  Before  precipitating  the  potassium  it  is 
necessary  to  remove  calcium,  aluminium,  etc.,  by  precipitation 
with  ammonium  hydroxide  and  ammonium  oxalate. 

All  platinum  residues  and  washings  from  this  determination 
should  be  saved. 

Procedure.  —  Weigh  a  sample  of  10  grams  of  the  material  and 
boil  in  a  casserole  with  300  c.c.  of  water  for  thirty  minutes. 
Without  filtering,  add  ammonium  hydroxide  in  slight  excess  to  the 
hot  solution,  then  add  slowly  a  sufficient  quantity  of  ammonium 


AGRICULTURAL  ANALYSIS  141 

oxalate  solution  to  precipitate  all  the  calcium  present.  Cool  the 
solution,  make  up  to  500  c.c.,  mix  thoroughly,  and  filter  through  a 
dry  filter,  discarding  the  first  10  c.c.  of  the  filtrate.  Place  50  c.c. 
of  the  filtrate  into  a  porcelain  dish,  evaporate  nearly  to  dryness, 
add  i  c.c.  of  sulphuric  acid  (sp.  gr.  1.4),  and  evaporate  to  dry- 
ness,  taking  care  that  the  solution  does  not  spatter.  Ignite 
the  residue  until  it  is  white.  As  the  potassium  is  all  in  the  form 
of  the  sulphate,  no  loss  from  volatilization  need  be  apprehended. 
Dissolve  the  residue  in  about  20  c.c.  of  hot  water.  If  the  solution 
is  perfectly  clear,  add  a  drop  or  two  of  hydrochloric  acid  and  a 
slight  excess  of  platinic  chloride  solution  (2-5  c.c).  If  the  solution 
is  not  clear,  filter  through  a  small  filter,  then  add  a  few  drops  of 
hydrochloric  acid,  and  then  the  platinic  chloride  solution.  Evapo- 
rate the  solution  in  a  small  dish  to  a  thick  paste  and  add  40  c.c. 
of  80  per  cent  alcohol.  Cover  the  dish  with  a  glass  and  allow  to 
stand  for  an  hour  or  two  in  a  place  which  is  free  from  the  fumes 
of  ammonia.  At  the  end  of  that  time  examine  the  supernatant 
liquid.  If  it  has  not  a  deep  yellow  color,  it  is  proof  that  an  in- 
sufficient amount  of  platinic  chloride  has  been  added.  When  the 
precipitate  has  settled,  pour  off  the  clear  liquid  through  a  prepared 
and  weighed  Gooch  crucible,  and  wash  the  precipitate  by  decanta- 
tion  with  80  per  cent  alcohol.  Bring  all  of  the  precipitate  upon  the 
filter  and  wash  with  alcohol  until  the  filtrate  is  colorless.  Then 
wash  three  times  more.  Now  run  through  the  filter  10  c.c.  of  the 
concentrated  ammonium  chloride  solution  which  has  been  saturated 
with  potassium  chlorplatinate.  Repeat  this  treatment  with  the 
ammonium  chloride  solution  five  times.  Wash  the  precipitate 
thoroughly  with  80  per  cent  alcohol,  heat  for  forty  minutes  at  135° 
in  the  air  bath,  cool,  and  weigh.  Heat  and  weigh  again.  When 
the  weight  is  constant,  calculate  the  weight  of  potassium  oxide 
from  the  weight  of  potassium  chlorplatinate.  Calculate  the  per- 
centages of  potassium  and  potassium  oxide  present  in  the  fertilizer. 

Notes.  —  i.  When  it  is  desired  to  determine  the  total  amount  of 
potassium  in  organic  substances,  such  as  cotton-seed  meal,  tobacco 
stems,  etc.,  saturate  10  grams  of  the  sample  with  strong  sulphuric 
acid,  evaporate  to  dryness,  and  heat  at  a  low  red  heat  until  the 
organic  matter  is  destroyed.  Add  a  little  strong  hydrochloric  acid, 
warm  slightly  in  order  to  loosen  the  mass  from  the  dish,  and  pro- 
ceed as  above. 


142  QUANTITATIVE  ANALYSIS 

2.  The    ammonium    hydroxide    and   ammonium    oxalate   com- 
pletely precipitate  all  of  the  bases  present  with  the  exception  of 
magnesium.     Owing  to  the  difficulty  of  complete  volatilization,  a 
large  excess  of  ammonium  oxalate  should  be  avoided. 

3.  Precipitates  of  aluminium  and  iron  hydroxide  have  a  marked 
tendency  to  occlude   potassium   salts.     This  may  be  avoided  by 
adding  the  precipitating  reagent  slowly  and  with  stirring. 

4.  Ammonia  forms  insoluble  ammonium  chlorplatinate  in  the 
presence  of  platinic  chloride.     It  is  therefore  necessary  to  protect 
the  solution  from  the  fumes  of  ammonia.     For  the  same  reason 
the  platinic  chloride  should  be  completely  washed  out  of  the  pre- 
cipitate  of    potassium    chlorplatinate    before   the   washing   with 
ammonium  chloride  solution  begins. 

5.  If  the  potassium  is  precipitated  from  too  concentrated  a  solu- 
tion, the  precipitate  will  contain  water  which  will  be  removed  with 
great  difficulty.     The  precipitation  should  take  place  in  a  fairly 
dilute  solution. 

6.  Potassium  chlorplatinate  is  somewhat  soluble  in  ammonium 
chloride  solutions.     Consequently  this  solution  must  be  saturated 
with  potassium  chlorplatinate  before  using.     The  ammonium  chlo- 
ride solution  removes  any  magnesium  salts  which  may  be  present 
with  the  precipitate. 

REFERENCES 

SNYDER,  Soils  and  Fertilizers  (1905). 

WILEY,  Principles  and  Practice  of  Agricultural  Analysis,  Vol.  II,  Fertilizers. 


THE  ANALYSIS  OF   SOIL 

Soil  may  be  defined  as  that  portion  of  the  earth's  surface  which 
permits,  under  proper  climatic  conditions,  the  growth  and  nourish- 
ing of  plants.  The  soil  proper,  or  top  soil,  may  extend  from  two 
or  three  inches  to  as  many  feet  below  the  surface  of  the  ground, 
the  portion  below  this  being  known  as  the  subsoil.  The  subsoil 
differs  from  the  soil  in  physical  properties,  also  in  its  chemical 
composition.  It  may  consist  of  rock  matter,  layers  of  sand, 
clay,  etc. 

Constituents  of  the  Soil 

Soil  is  a  heterogeneous  mixture  composed  of  disintegrated  rock, 
organic  matter  of  animal  and  vegetable  origin,  water,  occluded 


AGRICULTURAL  ANALYSIS  143 

gases,  and  certain  living  organisms  which  exert  a  considerable  in- 
fluence upon  vegetable  growth.  Of  the  total  number  of  elements 
there  are  only  about  twenty  found  in  soils  to  any  appreciable  extent. 
These  are  the  elements  found  in  the  common  forms  of  mineral 
matter,  and  those  which  are  present  in  organic  substances.  From 
the  standpoint  of  their  values  as  plant  foods,  the  elements  in  soils 
may  be  arranged  in  the  following  classes  : * 

I.  Essential  elements  most   liable   to   be   deficient.      Nitrogen, 
potassium,  phosphorus. 

These  may  be  present  in  the  following  forms : 
Nitrogen :  organic  nitrogen,  ammonium  salts,  nitrates. 
Potassium :  silicates,  such  as  orthoclase,  mica,  and  granite. 
Phosphorus :    phosphates    and    in    combination    with    organic 
matter. 

II.  Essential    elements    usually  abundant.     Iron,    magnesium, 
calcium,  and  sulphur. 

Iron  :  silicates  and  oxides. 

Magnesium :  carbonate  and  silicates. 

Calcium :  carbonate,  silicate,  phosphates,  and  sulphate. 

Sulphur  :  principally  as  sulphates. 

III.  Unnecessary   and    accidental   elements    usually    abundant. 
Aluminium,  iron,  silicon,  etc. 

Organic  Constituents 

Besides  the  soil  constituents  which  are  present  as  the  result  of 
the  disintegration  of  mineral  matter,  a  certain  amount  of  organic 
matter  is  always  present  and,  as  in  the  case  of  peaty  soils,  may  even 
be  the  predominating  constituent.  This  organic  matter  is  a  mix- 
ture of  substances  of  animal  and  vegetable  origin  and  exists  in 
various  stages  of  decomposition.  The  decaying  organic  matter 
plays  an  important  part  in  crop  production. 

The  active  principle  of  the  organic  matter  is  called  humus.  In 
general  this  may  be  considered  as  the  intermediate  decomposition 
products  of  the  organic  material.  Since  the  organic  constituents 
present  in  soils  may  differ  greatly  both  as  to  origin  and  chemical 
composition,  it  is  obvious  that  the  term  humus  is  indefinite. 
Among  the  organic  decomposition  products  are  certain  substances 
having  acid  properties  which  combine  with  basic  materials  in  the 
soil  and  form  organic  salts  which  are  known  as  humates.  Some  of 

1  This  classification  is  essentially  that  proposed  by  Snyder. 


144 


QUANTITATIVE  ANALYSIS 


the  important  humates  are  those  of  potassium  and  calcium,  which 
are  known  as  potassium  and  calcium  humates  respectively. 

The  following  table,  which  contains  the  results  of  the  analyses 
of  several  typical  soils,  illustrates  the  marked  differences  in  their 
chemical  composition : 

ULTIMATE  ANALYSIS  OF  TYPE  SOILS  OF  ILLINOIS  (COMPOSITE  SAMPLES) 
DRY  BASIS.     SURFACE  SOIL,  TOP  SEVEN  INCHES 


SANDY  SOIL 

PEATY 
SWAMPY 
SOIL 

EARLY 
WISCONSIN 
GLACIATION; 
YELLOW  SILT 
LOAM 
(TIMBER) 

EARLY 
WISCONSIN 
GLACIATION; 
BROWN  SILT 
LOAM 
(PRAIRIE) 

EARLY 
WISCONSIN 
GLACIATION; 
BLACK  CLAY 
LOAM 
(PRAIRIE) 

Nitrogen       .... 

.052 
.038 

1.24 

.509 
.185 
.642 

.835 
2.26 
1.64 
42.29 

3.58 
.I9I 
.289 

.299 
.628 
41.21 

1.07 
1.  06 

i-39 
448 

.099 
.040 
I.58 

.622 

•390 
1.  10 
.012 

I.78 

4.78 
.856 

37-77 

.266 
.059 
I.78 

.556 
.470 
3.20 
.005 

2.57 
5.98 

•549 
34-13 

•399 
.096 
1.65 

1.27 
.716 

444 
.026 

242 
6.29 
.678 
31-77 

Phosphorus  .... 
Potassium     .     .     .    w. 

Calcium 

Magnesium   .... 
Organic  carbon  .     .     . 
Inorganic  carbon    .     . 

Iron     

Aluminium    .... 
Sodium     

Silicon      .          ... 

Oxygen,  Hydrogen, 
Sulphur,  Manganese, 
Titanium,  etc.    . 

By  difference 

The  complete  examination  of  a  soil  includes  its  study  from 
chemical,  physical,  and  biological  standpoints.  The  chemical  ex- 
amination will  be  discussed  in  the  following  pages,  as  it  alone 
falls  within  the  scope  of  this  book. 


The  Collection  and  Preparation  of  the  Sample 

Remove  all  surface  accumulation  of  decaying  leaves  and  other 
foreign  matter  and  then  remove  a  layer  of  the  soil  of  uniform 
thickness  from  the  surface  to  the  desired  depth.  In  order  to 
eliminate  the  effects  of  accidental  variations  in  the  soil,  select 
specimens  from  five  to  six  places  in  the  field  and  remove  from 
each  place  several  pounds  of  the  soil,  to  the  depth  of  six  inches,  or 


AGRICULTURAL  ANALYSIS 


145 


Outline  for  the  Analysis  of  a  Sample  of  Soil 

Volatile  matter  ] 
Carbon  dioxide  I    Determined  in 
Humus  f       separate  samples. 

Nitrogen  J 

Determination  of  Acid-soluble  Substances 

Digest  10  grms.  of  soil  with  HC1  at  100°  for  10  hours. 
Filter. 


1 

Solution  (to  be  analyzed  for  Fe2O3,  AUO,,,  MnO, 
CaO,  MgO,  Na2O,  K2O,  SiO2,  I'-A,  SO3). 

Add  HNO3.     Evaporate  to  dryness,  dehydrate 
silica  at  100°.     Dissolve  bases  in  HC1.     Filter. 

Residue  (i). 
Silicates,  organic  matter,  etc. 

Unite  residues  i, 
•2,  and  3,  ignite  to 
constant  weight, 

r 

Solution. 
Evaporate  to  dryness  and  dehydrate.     Dissolve 
and  filter. 

Residue  (2). 
SiO2  (traces  of  AI2O3+Fe2O3). 

insoluble  matter 
+  soluble  silica. 

Solution. 

Make  up  to  a  volume  of  500  c. 

Label  "  Solution  A." 


Residue  (3). 

SiO2,  with  traces  of  FejO3 

and  A12O3. 


Analysis  of  Solution  A 


Determination  of  (AUO3+  Fe2O3+  P2O5)    Determination  of  SO3,  Fe2O3, 


MnO,  CaO,  and  MgO. 

Use  too  c.c.  of  solution  A. 

Make  alkaline  with  NH4OH.     Filter. 


Na2O  and  K2O.     Concentrate 
loo  c.c.  of  solution  A,  add 
BaCl2.     Filter. 


Filtrate. 
Boil  with  Br  water. 
Acidify  with  acetic 
acid.     Filter. 

I 

Ppt.     Ignite 
and  weigh 
Al203+Fe203+P205. 
Determine  A12O3 
by  difference 
after  determining 
Fe2O3  and  P2O6. 

Filtrate. 

Add  NH4 
Filter. 

Filtrate. 
Evaporat 
dryness  t 
ammoniu 
Add  Ba(( 
Filter. 

Filtrate. 
AddNH 
(NH4)2C 
Filter. 

Filtrate. 
Evapora 
dryness, 
ammonii 
weigh  N 
Dissolve 
chlorides 
Add  PtC 
and  alco 
on  a  Goc 

Filtrate. 
D  is  car  a 

Dis 
Ppt  BaSO4.          Mg 
OH.               Ignite  and             P  a- 
weigh. 

Ppt. 
e  to               A1(O 
o  expel         Diss( 
m  salts.         Dete 
DH)2.            titrat 
K2Cr 

ofFe(OH)3, 
H)3,  etc. 
>lve  in  HC1. 
rmine  Fe  by 
ion  with 
207. 

Filtrate.                         Ppt.  MnO2. 
Add  NH4OH  and        Ignite  and  weigh 
(NH4)2C204.                Mn304. 
Dissolve  ppt.  in 
HC1  and  re-ppt. 
withNH4OH.    Filter. 

Filtrate. 
Ppt.  MgNH4P04  in 
the  usual  manner. 
Ignite  and  weigh 
Mg,P207. 

Ppt.  CaC,04. 
Ignite.     Change 
to  CaSO4  and 
weigh. 

Ppt.  ofMg(OH)8. 
,OH+           Discard. 
03. 

Ppt. 
te  to               Disc 
expel 
m  salts  and 
aCl+  KCl. 
mixed 
in  water. 
I4  solution 
hoi.     Filter 
ch  crucible. 

ofBaCO3. 
ard. 

Ppt.  K2PtCl6. 
'.                     Weigh  and  calculate 
NaCl  by  difference. 

3 

Determination  of 
P2O5.     Concentrate 
200  c.c.  of  Solution 
A.    Ppt.  the  P  as 
(NH4)3PO4  . 12  MoO3. 
Dissolve  and  ppt.  as 
MgNH4P04.     Weigh 
P  as  Mg2P2O7. 


146  QUANTITATIVE  ANALYSIS 

to  the  change  between  the  surface  soil  and  the  subsoil,  in  case 
such  change  occurs  between  the  depth  of  six  and  twelve  inches. 
In  no  case  should  the  sample  be  taken  to  a  greater  depth  than 
twelve  inches.  If  the  surface  soil  extends  to  a  greater  depth,  a 
separate  sample  below  the  depth  of  twelve  inches  should  be  taken 
if  a  thorough  study  of  the  soil  is  desired.  If  the  surface  soil  ex- 
tends to  a  depth  of  less  than  six  inches,  and  the  difference  between 
it  and  the  subsoil  is  unusually  great,  a  separate  sample  of  the  sur- 
face soil  should  be  obtained  besides  the  one  to  the  depth  of  six 
inches. 

Mix  all  the  samples  of  the  surface  soils  thoroughly,  remove  all 
stones,  shake  out  roots  and  foreign  matter,  and  expose  the  soil  in 
thin  layers  in  a  warm  room  until  thoroughly  air  dry,  or  dry  it  in 
an  air  bath  at  40°.  The  soil  should  be  dried  rapidly,  but  it  should 
not  be  heated  above  40°,  because  of  the  danger  of  breaking  up  the 
ammonium  compounds  or  making  some  of  the  compounds  present 
more  insoluble.  After  drying,  all  lumps  should  be  finely  pulver- 
ized, the  soil  thoroughly  mixed,  spread  out  upon  a  clean  paper 
and  200  grams  taken  from  different  parts  of  the  sample  and  sifted 
through  a  sieve  with  circular  openings  \  mm.  in  diameter.  If 
necessary,  rub  the  soil  gently  in  a  mortar  with  a  pestle  until  the 
fine  earth  has  been  separated  as  completely  as  possible  from  the 
particles  that  are  too  coarse  to  pass  the  sieve.  Mix  the  fine  soil 
which  passes  through  the  sieve,  place  in  a  tightly  stoppered  bot- 
tle, and  use  for  the  analysis.  The  coarse  part  should  be  weighed 
and  bottled. 

Note. — As  a  result  of  bacterial  action  certain  constituents  of  the 
soil  are  constantly  undergoing  changes.  The  organic  nitrogen, 
for  example,  is  continually  being  oxidized  to  the  more  available 
forms,  nitrates  and  nitrites.  This  change  is  termed  nitrification. 
Because  of  these  changes  it  is  necessary  to  avoid  prolonged  dry- 
ing. 

Moisture 

Procedure. —  Place  from  two  to  four  grams  of  the  air-dried  soil 
into  a  weighed  porcelain  dish  and  heat  for  five  hours  at  100°. 
Cool  in  a  desiccator  and  weigh  rapidly  to  avoid  absorption  of  mois- 
ture from  the  air.  Repeat  the  heating,  cooling,  and  weighing  at 
intervals  of  two  hours  until  constant  weight  is  found,  and  estimate 
the  moisture  by  loss  of  weight. 


AGRICULTURAL  ANALYSIS  147 

Volatile  Matter 

Procedure.  —  Heat  the  dish  and  dry  soil  from  the  above  determi- 
nation to  full  redness,  until  all  organic  matter  is  burned.  If  the 
soil  contains  any  carbonates,  the  contents  of  the  dish,  after  cooling, 
should  be  moistened  with  a  few  drops  of  a  saturated  solution  of 
ammonium  carbonate,  dried  and  heated  to  dull  redness  to  expel 
ammonium  salts,  cooled  in  the  desiccator,  and  weighed. 

Notes.  —  i .  The  addition  of  ammonium  carbonate  changes  any 
calcium  oxide  formed  during  the  ignition  back  into  the  carbonate. 

2.  The  loss  in  weight  in  the  above  determination  is  due  to  the 
following  causes : 

(a)  The  ignition  of  the  organic  matter. 

(b)  Volatilization  of  ammonium  salts  and  of  water  of  combina- 
tion. 

(c)  The  decomposition  of  magnesium  carbonate  with  the  forma- 
tion of  magnesium  oxide,  which  is  not  readily  changed  back  to  the 
carbonate,  also  the  fact  that  the  calcium  originally  present  as  the 
humate  is  changed  to  the  carbonate. 

3.  A  certain  increase  in  weight  is  caused  by  the  oxidation  of 
any   ferrous   iron.     This   tends   to   counterbalance   some   of   the 
above-mentioned  losses. 

4.  Because  of  the  variety  of  factors  to  which  the  loss  on  ignition 
is  due,  it  is  evident  that  this  determination  gives  but  an  approxi- 
mate idea  of  the  amount  of  organic  matter  present.     The  determina- 
tion of  the  total  organic  carbon  has  recently  been  used  for  the 
estimation  of  the  organic  matter  in  soils.     The  method  is  described 
by  Pettit  and  Schaub,  Jour.  Am.  Chem.  Soc.,  26,  1640  (1904), 

The  Extraction  of  the  Acid-soluble  Material 

It  is  well  known  that  the  materials  present  in  soils  are  not  all 
available  as  plant  food.  Potassium,  for  example,  may  exist  as  the 
easily  available  carbonate,  or  it  may  be  present  as  a  feldspar 
which  is  of  little  immediate  value  in  aiding  the  growth  of  plants. 
It  is,  therefore,  the  usual  practice,  when  analyzing  a  soil,  to  deter- 
mine the  amount  of  available  plant  food  rather  than  its  total  quan- 
tity, although  this  latter  determination  is  often  of  value.  Numerous 
solvents  have  been  suggested  for  the  extraction  of  the  plant  food 
from  the  soil,  but  none  of  them  imitates  the  extraction  under 


148  QUANTITATIVE  ANALYSIS 

natural  conditions.  The  following  method,  recommended  by  the 
Association  of  Official  Agricultural  Chemists,  in  which  hydrochloric 
acid  is  used  as  a  solvent,  is  of  value  in  showing  approximately  the 
limit  of  the  solvent  action  of  the  roots  of  plants. 

Procedure.  —  Place  ten  grams  of  the  air-dried  soil  into  an  Erlen- 
meyer  flask  of  about  200  c.c.  capacity,  add  100  c.c.  of  pure 
hydrochloric  acid  of  specific  gravity  1.115,  insert  a  rubber  stopper 
carrying  a  hard-glass  condensing  tube  about  \  inch  internal  diameter 
and  about  30  inches  long.  If  sulphuric  acid  is  to  be  determined 
in  the  solution,  a  flask  with  a  ground-glass  stopper  carrying  a  con- 
densing tube  must  be  used.  Place  the  flask  in  a  water  bath,  being 
sure  that  it  is  immersed  in  the  water  at  least  to  the  level  of  the 
acid  and  that  the  water  is  kept  boiling  during  the  digestion.  Di- 
gest continuously  for  ten  hours  at  the  temperature  of  boiling  water, 
shaking  once  each  hour.  Decant  the  clear  liquid  from  the  flask 
into  a  medium-sized  casserole  and  wash  the  residue  out  of  the 
flask  with  distilled  water  upon  a  filter,  adding  the  washings  to 
the  acid  liquid  in  the  casserole.  Thoroughly  wash  the  residue 
free  from  acid  and  then  dry  it  and  save  it  for  ignition  as  directed 
below. 

Notes.  —  i .  The  amount  of  material  dissolved  by  the  acid  varies 
with  the  length  of  time  of  heating,  the  temperature  and  the  strength 
of  the  acid  employed,  and  the  fineness  of  the  material.  Conse- 
quently, the  directions  given  above  should  be  closely  followed. 

2.  By  the  action  of  the  hydrochloric  acid  solution  on  the  soil, 
the    following    constituents   are   dissolved :     ferrous     and    ferric 
oxides,  ferrous  carbonate,  manganese  oxides,  calcium  and  magne- 
sium  carbonates,   calcium   sulphate  and  phosphates,  and   certain 
silicates,    such   as   those  of   aluminium,   calcium,   and  potassium. 
Certain  forms  of  organic  matter  are  also  dissolved. 

3.  The  residue  is  composed  for  the  greater  part  of  crystallized 
and  amorphous  silica  and  silicates  of  Fe,  Mn,  Al,  Ca,  Mg,  K,  Na. 
Certain  forms  of  organic  matter  are  also  present  in  the  residue. 

Removal  of  Soluble  Silica  from  Solution 

Principle.  —  On  evaporating  a  solution  of  silicic  acid  to  dryness 
and  heating  at  100°  it  is  dehydrated  and  rendered  insoluble  in  dilute 
acids. 


AGRICULTURAL  ANALYSIS  149 

Procedure,  —  Add  about  5  c.c.  of  concentrated  nitric  acid  to  the 
filtrate  from  the  insoluble  matter  in  order  to  oxidize  the  organic 
matter  present  and  evaporate  to  dryness  on  the  steam  bath  until 
no  more  fumes  of  hydrochloric  acid  are  given  off,  the  residue  being 
left  in  the  form  of  a  dry,  dark-brown  powder.  Add  5  c.c.  of  con- 
centrated hydrochloric  acid  to  the  casserole,  allow  to  stand  for  a 
few  minutes  to  insure  the  solution  of  the  basic  salts,  and  add  100 
c.c.  of  distilled  water.  Heat  to  boiling,  filter  through  an  ashless 
filter,  wash  with  hot  water  containing  a  little  hydrochloric  acid, 
and  wash  finally  with  hot  water  alone  until  the  residue  is  free  from 
chlorides.  Evaporate  the  filtrate  to  dryness  and  treat  exactly  as 
before,  using,  however,  a  new  filter  for  the  filtration.  Cool  the 
filtrate,  make  up  to  500  c.c.,  and  label  the  solution  "  A." 

Notes. —  i.  For  the  complete  removal  of  silica  from  solution,  the 
following  conditions  should  be  closely  observed: 

a.  Two  dehydrations  of  the  silica  should  be  made,  since  it  has 
been  found  that  only  95  per  cent  of  the  silica  present  is  removed 
by  one  dehydration.     An  intermediate  filtration  between  the  two 
dehydrations  has  been  found  necessary. 

b.  The  silica  may  be  completely  dehydrated  on  the  water  bath, 
although  many  chemists  prefer  to  heat  finally  at   110°  or   120°. 
Heating  above   120°   renders   insoluble    appreciable   amounts   of 
alumina  and  ferrie  oxide  which  cannot  be  dissolved  by  long  diges- 
tion with  hydrochloric  acid.     Moreover,  at  higher   temperatures 
magnesia  recombines  with  silica  with  the  formation  of  magnesium 
silicate,  which  is  decomposed  by  hydrochloric  acid  with  the  for- 
mation of  soluble  silicic  acid. 

2.  The  precipitate  should  be  first  washed  with  hot  water  acidi- 
fied with  a  few  cubic  centimeters  of  hydrochloric  acid.  This  will 
prevent  the  separation  of  insoluble  iron  salts,  which  would  take 
place  if  hot  water  alone  were  used. 

Insoluble  Matter  and  Soluble  Silica 

Procedure.  —  Add  the  silica  residues  from  solution  "  A  "  to  the 
main  insoluble  residue,  ignite  in  the  blast  the  combined  residues 
together  with  the  filters  in  a  large  weighed  porcelain  crucible  and 
weigh.  Heat  to  constant  weight.  From  the  weight  of  this  resi- 
due calculate  the  percentage  of  insoluble  matter  plus  the  soluble 
silica. 


ISO  QUANTITATIVE  ANALYSIS 

The  Determination  of  the  Acid-soluble  Substances 
Iron,  Aluminium ,  and  Phosphorus  Collectively 

Procedure. — To  100  c.c.  of  solution  "A"  add  ammonium  hy- 
droxide until  the  solution  is  slightly  alkaline,  observing  the  pre- 
cautions given  under  the  determination  of  aluminium,  page  37. 
Drive  off  the  excess  of  ammonia  by  boiling,  allow  the  precipitate 
to  settle,  and  decant  the  clear  solution  through  a  filter.  Add'  50 
c.c.  of  hot  distilled  water,  boil,  allow  to  settle,  and  decant  as  before. 
After  pouring  off  all  the  clear  solution  possible,  dissolve  the  resi- 
due with  a  few  drops  of  nitric  acid,  and  precipitate  again  with 
ammonium  hydroxide  as  before.  Wash  by  decantation,  transfer 
all  the  precipitate  to  the  filter,  and  wash  with  hot  distilled  water 
containing  a  little  ammonium  nitrate,  until  the  washings  are  free 
from  chlorides.  Dry  the  filter  and  precipitate,  separate  the  pre- 
cipitate from  the  filter,  burn  the  filter  and  add  to  the  ash  the 
precipitate,  ignite  the  crucible  to  bright  redness,  cool  in  a  desicca- 
tor, and  weigh.  The  weight  of  the  ignited  precipitate  minus  the 
weight  of  the  iron  oxide  and  phosphorus  pentoxide  (found  in 
separate  determinations)  represents  the  weight  of  the  aluminium 
oxide. 

Notes.  —  i.  The  separation  of  iron  and  aluminium  from  the 
divalent  metals  is  not  complete  by  one  precipitation,  a  small 
amount  of  magnesium  invariably  precipitating  at  the  same  time. 
It  is  necessary,  therefore,  to  make  a  second  precipitation. 

2.  The  ammonium  hydroxide  used  must  be  free  from  the  car- 
bonate, which  would  precipitate  some  of  the  calcium  with  the  iron 
and  aluminium. 

3.  If  the  precipitate  is  not  washed  completely  free  from  chlo- 
rides, there  is  danger  of  volatilization  of  the  chlorides  of  iron  and 
aluminium  upon  ignition   of   the   precipitate.      To  facilitate   the 
removal  of  the  chlorides,  the  precipitate  is  redissolved  in  nitric 
instead  of  hydrochloric  acid. 

4.  In  the  presence  of   hot  carbonaceous  matter,   ferric  oxide 
is  partially  reduced  to  the  magnetic  oxide  (Fe3O4),  which  cannot 
be  completely  changed  back  to  the  ferric  oxide,  even  by  treatment 
with  oxidizing  agents.     To  avoid  this  reduction,  it  is  necessary  to 
ignite  the  filter  separate  from  the  precipitate. 


AGRICULTURAL  ANALYSIS  151 

Iron 

See  the  determination  of  sodium  and  potassium  on  page  1 54. 

Phosphorus 

Procedure.  —  Evaporate  200  c.c.  of  solution  "  A  "  to  about  75  c.c., 
nearly  neutralize  with  ammonium  hydroxide,  and  add  about  10 
grams  of  pure  crystallized  ammonium  nitrate.  Add  gradually 
about  20  c.c.  of  ammonium  molybdate  solution  and  digest  at  40°. 
When  the  precipitate  has  settled,  remove  with  a  pipette  about  5  c.c. 
of  the  clear  liquid  and  test  it  by  allowing  it  to  run  into  5  c.c.  of 
warm  molybdate  solution.  If  any  precipitate  is  produced,  the 
test  liquid  should  be  returned  to  the  main  portion,  more  molybdate 
solution  added,  and  the  digestion  continued.  After  standing  from 
eight  to  twelve  hours  at  a  temperature  not  above  40°,  filter  the 
ammonium  phosphomolybdate  and  determine  the  phosphorus  as 
magnesium  pyrophosphate,  as  described  under  the  determination 
of  the  total  phosphorus  in  fertilizers,  page  134.  Express  the  re- 
sults as  phosphorus  and  phosphorus  pentoxide. 

Manganese 

Principle.  —  When  bromine  water  is  added  to  an  alkaline  solution 
of  a  manganese  salt,  upon  boiling,  the  manganese  is  precipitated 
as  a  hydrated  manganese  dioxide.  Upon  ignition  the  manganese 
dioxide  is  changed  to  Mn3O4. 

3  Mn02  (ignited)  =  Mn3O4  +  O2. 

Procedure.  —  Concentrate  the  filtrate  from  the  determination  of 
iron,  aluminium,  and  phosphorus  to  about  75  c.c.,  make  alkaline 
with  ammonium  hydroxide,  add  bromine  water,  and  heat  to  boiling, 
keeping  the  beaker  covered  with  a  cover-glass.  When  most  of 
the  bromine  has  been  driven  off,  allow  the  beaker  to  cool  some- 
what, add  more  ammonium  hydroxide  and  bromine  water,  and  heat 
again.  Continue  this  process  until  the  manganese  is  completely 
precipitated,  which  requires  from  fifteen  to  thirty  minutes.  Acid- 
ify the  solution  with  a  few  drops  of  acetic  acid,  filter  while  still 
hot,  wash  the  precipitate  with  hot  water,  dry,  ignite,  and  weigh 
as  Mn3O4.  Compute  the  percentage  of  manganese  in  the  soil. 

Note.  —  By  strong  ignition  manganese  dioxide  is  converted  to 
mangano-manganic  oxide  Mn3O4.  The  exact  composition  of  the 


152  QUANTITATIVE  ANALYSIS 

ignited  precipitate  varies  with  the  conditions  under  which  the  igni- 
tion takes  place.  With  small  quantities  of  manganese  the  varia- 
tion is  so  small  that  it  may  be  neglected.  Large  precipitates  of 
manganese  dioxide  should  be  redissolved  in  a  solution  of  sulphu- 
rous acid,  precipitated  from  an  ammoniacal  solution  as  manganese 
ammonium  phosphate  and  weighed  as  manganese  pyrophosphate. 

Calcium 

Procedure.  —  Evaporate  the  filtrate  from  the  manganese  deter- 
mination to  about  50  c.c.,  make  slightly  alkaline  with  ammonium 
hydroxide,  and  precipitate  with  ammonium  oxalate.  Heat  to  boil- 
ing, digest,  and  decant  the  clear  solution  upon  a  filter.  Pour  from 
15  to  20  c.c.  of  hot  distilled  water  upon  the  precipitate,  and  again 
decant.  Dissolve  the  precipitate  in  the  beaker  with  a  few  drops 
of  hydrochloric  acid,  add  a  little  water,  and  reprecipitate.  Filter 
through  the  same  filter  as  before,  wash  the  precipitate  free  from 
chlorides,  dry,  ignite,  convert  to  calcium  sulphate,  and  weigh. 
Calculate  the  percentage  of  calcium  in  the  soil. 

Note.  —  Read  the  notes  on  the  separation  of  calcium  and  mag- 
nesium, page  34. 

Magnesium 

Procedure.  —  Slightly  acidify  the  filtrate  and  washings  from  the 
determination  of  calcium  with  hydrochloric  acid,  concentrate  to 
about  50  c.c.,  and  make  slightly  alkaline  with  ammonium  hydrox- 
ide. Add  10  c.c.  of  microcosmic  salt  solution,  allow  to  stand  for 
a  few  minutes,  then  add  one-third  the  volume  of  ammonium 
hydroxide  solution.  Allow  to  stand  for  twelve  hours ;  filter  off 
the  magnesium  ammonium  phosphate.  Dissolve  the  precipitate 
in  hydrochloric  acid  and  reprecipitate.  Ignite  the  precipitate  and 
weigh  as  magnesium  pyrophosphate.  Express  results  as  mag- 
nesium. 

Sulphur 

Procedure.  —  Evaporate  100  to  150  c.c.  of  solution  "  A  "  nearly  to 
dryness  on  a  water  bath,  then  add  50  c.c.  of  water  and  determine 
the  sulphur  by  precipitating  and  weighing  as  barium  sulphate 
as  described  under  Exercise  VI,  page  29. 

Note.  —  The  precipitate  is  appreciably  soluble  in  concentrated 
hydrochloric  acid,  hence  the  necessity  of  expelling  the  excess  of 
acid  by  evaporation. 


AGRICULTURAL  ANALYSIS  153 

Iron,  Potassium,  Sodium 

Procedure. — Add  ammonium  hydroxide  to  the  filtrate  from  the 
determination  of  sulphur,  and  precipitate  exactly  as  in  the  deter- 
mination of  iron,  aluminium,  and  phosphorus  collectively. 

Wash  the  precipitate  free  from  chlorides,  dissolve  it  in  hydro- 
chloric acid  and  estimate  the  iron  present  by  titrating  with  standard 
dichromate  solution.  Calculate  the  percentage  of  iron  in  the 
soil.  Evaporate  the  filtrate  and  washings  from  the  precipitate  to 
dryness  on  the  water  bath  in  a  small  casserole,  heat  cautiously  for 
an  hour  at  110°,  to  avoid  decrepitation  due  to  incomplete  drying, 
then  heat  at  a  low  red  heat  until  the  ammonium  salts  are  expelled, 
holding  the  casserole  in  the  hand.  Dissolve  the  residue  in  about 
25  c.c.  of  hot  water,  add  5  c.c.  of  a  saturated  barium  hydroxide 
solution  and  heat  to  boiling.  Allow  the  precipitate  to  settle  and 
test  the  supernatant  liquid  for  complete  precipitation  with  a  few 
drops  of  barium  hydroxide.  When  no  further  precipitate  is  pro- 
duced, filter,  and  wash  thoroughly  with  hot  water.  Add  ammonium 
hydroxide  and  ammonium  carbonate,  to  precipitate  the  barium. 

Allow  to  stand  a  short  time  on  the  water  bath,  filter,  wash  the 
precipitate  with  hot  water,  and  evaporate  the  filtrate  and  washings 
to  dryness  in  a  casserole.  Expel  the  ammonium  salts  as  before 
by  first  heating  at  no0,  then  over  the  flame  at  a  low  red  heat, 
dissolve  the  residue  in  a  little  water,  add  a  few  drops  of  ammonium 
hydroxide  and  a  drop  or  two  of  ammonium  carbonate  solution, 
let  stand  on  the  water  bath  for  a  few  minutes,  and  filter  into  a 
weighed  platinum  dish.  Evaporate  to  dryness  on  the  water  bath 
(heat  at  iio°-i2O°  for  half  an  hour)  and  heat  with  a  free  flame  at 
a  dull  red  heat  until  the  ammonium  salts  are  expelled  and  the 
residue  just  begins  to  fuse.  This  part  of  the  procedure  must  be 
carried  out  with  extreme  care.  The  burner  should  be  held  in  the 
hand,  the  flame  continually  moved  about  the  bottom  of  the  plati- 
num dish  in  order  to  prevent  the  volatilization  of  the  alkali  chlorides. 
The  weight  of  the  residue  represents  potassium  and  sodium  chlo- 
rides. 

Separation  of  Potassium  from  Sodium 

Principle.  —  If  an  excess  of  a  solution  of  platinic  chloride  is 
added  to  a  solution  of  sodium  and  potassium  chlorides  and  alcohol 
then  added,  potassium  chlorplatinate  is  precipitated,  while  sodium 


154  QUANTITATIVE  ANALYSIS 

chlorplatinate  remains  in  solution.  Since  sodium  chloride  is  insol- 
uble in  alcohol,  it  is  necessary  to  add  enough  of  the  platinic 
chloride  to  change  both  the  sodium  and  the  potassium  chlorides 
to  the  chlorplatinates. 

Procedure.  —  Dissolve  the  combined  weighed  chlorides  in  about 
10  c.c.  of  water.  If  they  do  not  go  completely  into  solution,  filter, 
wash,  evaporate  the  filtrate  in  a  platinum  dish  as  before,  and  weigh 
again.  The  solution  in  water  must  be  complete.  When  the  com- 
bined chlorides  dissolve  completely,  transfer  the  solution  to  a  small 
porcelain  dish.  Add  enough  platinic  chloride  solution  (containing 
o.i  gram  of  platinum  per  cubic  centimeter)  to  combine  with  the 
residue  to  form  the  chlorplatinate,  assuming  that  this  residue  is 
composed  entirely  of  sodium  chloride.  Evaporate  to  a  pasty 
consistency  on  a  water  bath,  then  pour  into  the  dish  about  50  c.c.  of 
80  per  cent  alcohol  and  heat  the  dish  and  contents  for  two  or  three 
minutes  upon  the  water  bath.  Stir  well  and  then  allow  to  stand 
for  at  least  two  hours  in  a  cool  place,  inverting  a  beaker  over  the 
dish,  or  by  some  other  means  protecting  it  from  possible  access  of 
ammonia  vapors.  Pour  off  the  clear  liquid  through  a  weighed 
Gooch  crucible,  filter  and  wash  the  precipitate  by  decantation, 
using  small  quantities  of  80  per  cent  alcohol.  Bring  the  potassium 
chlorplatinate  upon  the  filter  and  wash  completely  by  applying 
repeatedly  small  quantities  of  the  alcohol.  Dry  the  filter  and  con- 
tents to  constant  weight  at  1 3 5°.  Calculate  the  weight  of  the  potas- 
sium chlorplatinate  to  potassium  chloride.  Deduct  the  weight  of 
the  potassium  chloride  from  the  weight  of  the  mixed  chlorides. 
From  the  weights  of  the  chlorides  calculate  the  percentages  of 
potassium  oxide  and  sodium  oxide  in  the  soil,  also  the  percentages 
of  potassium  and  sodium. 

Humus 

Principle. — The  soil  is  leached  with  cold  dilute  hydrochloric 
acid,  which  dissolves  calcium  and  magnesium  salts.  By  the  re- 
moval of  these  substances,  the  humus  is  left  in  a  form  which  is 
easily  changed  to  a  soluble  ammonium  compound.  It  is  washed 
out  of  the  soil  by  means  of  dilute  ammonium  hydroxide,  the  solution 
is  evaporated  to  dryness,  weighed,  ignited,  and  the  loss  of  weight 
calculated  as  humus. 

Procedure.  —  Place  ten  grams  of  the  sample  in  a  prepared  Gooch 
crucible,  extract  with  one  per  cent  hydrochloric  acid  until  the 


AGRICULTURAL  ANALYSIS  155 

filtrate  gives  no  test  for  calcium,  and  remove  the  acid  by  washing 
with  water.  Wash  the  contents  of  the  crucible  (including  the 
asbestos  filter)  with  four  per  cent  ammonium  hydroxide  into  a 
500  c.c.  glass-stoppered  cylinder,  make  up  to  the  mark  with  the 
ammonium  hydroxide  and  allow  to  remain,  with  occasional  shaking, 
for  twenty-four  hours.  During  this  time  the  cylinder  should  be 
inclined  as  much  as  possible  without  bringing  the  contents  in  con- 
tact with  the  stopper,  thus  allowing  the  soil  to  settle  upon  the  side 
of  the  cylinder  and  exposing  a  large  surface  to  the  action  of  the 
ammonium  hydroxide.  Place  in  a  vertical  position  for  twelve 
hours  to  allow  the  sediment  to  settle,  then  filter  the  supernatant 
liquid  through  a  dry  filter.  Evaporate  100  c.c.  of  the  filtrate  to 
dryness,  dry  to  constant  weight  at  100°,  ignite  in  the  ash  muffle, 
and  weigh.  The  difference  in  weight  between  the  dried  and  the 
ignited  residues  is  humus. 

Notes.  —  i.  The  chemical  nature  of  humus  is  very  imperfectly 
known.  Several  distinct  bodies  having  acid  characters  have  been 
obtained  from  the  humus,  but  very  little  is  known  of  their  compo- 
sitions or  properties. 

2.  The  ammonium  compound  of  humic  acid  is  very  soluble  in 
water,  while  the  calcium  compound  is  insoluble. 

Total  Nitrogen  in  the  Presence  of  not  More  than  a  Trace  of  Nitrates 

Procedure.  —  Place  from  7  to  14  grams  of  the  soil  in  a  500  c.c. 
Kjeldahl  digestion  flask,  add  30  c.c.  of  strong  sulphuric  acid  or 
more  if  necessary,  and  about  0.65  gram  of  mercury.  Digest  for 
an  hour  and  if  necessary  oxidize  the  residue  with  potassium  per- 
manganate in  the  usual  way.  Cool,  add  to  the  flask  about  100  c.c. 
of  nitrogen-free  water,  shake  vigorously,  allow  the  sediment  to 
subside,  and  filter  through  ignited  asbestos  into  an  800  c.c.  Kjeldahl 
flask,  or  proceed  according  to  Note  2.  The  filter  is  easily  prepared 
by  placing  a  few  short  pieces  of  glass  tube  into  the  bottom  of  a 
Gooch  funnel  and  covering  them  with  a  thin  layer  of  the  ignited 
asbestos.  The  filtration  may  be  accelerated  by  fitting  the  funnel 
by  means  of  a  two-hole  cork  in  the  neck  of  a  Kjeldahl  flask  and 
connecting  with  the  suction.  Wash  the  residue  in  the  flask  at  least 
a  dozen  times  with  portions  of  25  c.c.  of  hot  nitrogen-free  water, 
and  determine  the  ammonia  by  distilling  in  the  usual  manner. 
Calculate  the  percentage  of  nitrogen  in  the  soil. 


156  QUANTITATIVE  ANALYSIS 

Notes. —  i.  If  the  soil  contains  more  than  a  trace  of  nitrates,  the 
modified  Kjeldahl  process  described  under  the  determination  of  the 
total  nitrogen  in  fertilizers,  page  138,  must  be  used. 

2.  If  the  solid  residue  left  after  digesting  the  soil  is  not  removed, 
on  distilling  the  ammonia  violent  explosions  will  be  caused  by 
"  bumping."  The  bumping  may  also  be  prevented  by  transferring 
the  entire  contents  of  the  digestion  flask  to  a  copper  distilling  flask 
(see  Fig.  31)  and  proceeding  as  usual. 

Carbon  Dioxide 

The  Apparatus.  —  For  this  determination  the  apparatus  shown  in 
Fig.  32  has  been  found  to  give  satisfactory  results.     It  consists 
essentially  of  a  flask  C,  into  which  the  sample  is  placed.     This  is 
provided  with  a  two-hole  rubber  stopper  which  carries  a  Hopkins 
condenser  D,  and   a    dropping   funnel    B  by 
means  of  which  dilute  acid  can  be  introduced 
into  the  flask.    The  carbon  dioxide  gas  evolved 
first    passes    through     the    condenser,    then 
through  the   U-tube  E  which   contains   glass 
beads    and    a   few   cubic  centimeters    of    sul- 
phuric acid  (sp.  gr.   1.4)  saturated  with  silver 
sulphate,  the  function  of  which  is  to  remove 
hydrochloric  acid  gas.     It  is  dried  by  passing 
I  j     into  the  U-tube  /''which  is  filled  with  calcium 

^*- S       chloride,  and  is  finally  absorbed  in  the  weighed 

Geissler  bulb  G  which  is  filled  with  potassium 
hydroxide  solution.  The  last  traces  of  carbon  dioxide  are  expelled 
from  the  apparatus  by  replacing  it  with  air  which  has  been  freed 
from  carbon  dioxide  by  passing  it  through  the  soda-lime  tube  A. 
To  draw  the  air  through  the  apparatus,  water  is  allowed  to  run 
from  the  bottle  K  into  L,  which  should  be  placed  about  five  feet 
lower  than  K.  This  process  is  termed  Aspiration. 

Procedure.  — Weigh  out  two  samples  of  from  five  to  ten  grams  of 
the  soil  into  clean  dry  flasks  of  250  c.c.  capacity.  Fill  two  Geissler 
potash  bulbs  with  a  solution  of  potassium  hydroxide  (350  grams 
per  liter)  so  that  the  bulbs  are  two-thirds  full,  and  fill  the  drying 
tubes  with  fresh  granular  calcium  chloride.  Provide  the  open  ends 
of  the  bulbs  with  caps  made  of  short  pieces  of  rubber  tubing  about 
I \  inches  long,  closed  with  a  short  piece  of  glass  rod.  Put  these  caps 
in  place,  wipe  the  bulbs  with  a  clean  cloth,  and  allow  them  to  stand 


AGRICULTURAL  ANALYSIS 


157 


158  QUANTITATIVE  ANALYSIS 

in  the  balance  case  for  twenty  minutes.  Remove  the  caps  to 
equalize  any  pressure  on  the  inside  of  the  bulbs,  replace  them  and 
weigh  accurately.  Attach  the  potash  bulb  to  the  apparatus  as 
shown  in  the  figure,  then  place  the  soda-lime  tube  H  between  the 
absorption  bulbs  and  the  aspirator,  which  should  be  full  of  water. 
Be  sure  that  all  rubber  connections  are  tight.  Examine  the  stem 
of  the  dropping  funnel  for  drops  of  acid  which  might  fall  into  the 
flask,  wipe  it  dry  if  necessary,  and  attach  the  flask. 

Test  the  apparatus  for  tightness  by  closing  the  cock  in  the  drop- 
ping funnel  and  opening  the  pinchcocky  which  connects  with  the 
aspirator.  If  the  apparatus  has  no  leaks,  bubbles  will  pass  through 
the  absorption  bulb  for  a  minute  or  two  and  then  cease.  When  it 
is  evident  that  the  apparatus  is  tight,  close  the  pinchcock  on  the 
aspirator  tube  and  equalize  the  pressure  in  the  flask  by  carefully 
opening  the  cock  in  the  funnel.  Disconnect  the  aspirator  from  the 
guard  tube.  Close  the  funnel  cock,  place  into  the  funnel  50  c.c.  of 
hydrochloric  acid  (sp.  gr.  1.12),  put  the  guard  tube  A  in  place,  and 
allow  two  or  three  drops  of  hydrochloric  acid  to  run  into  the  flask. 
Carbon  dioxide  gas  will  be  evolved  and  bubbles  will  be  forced 
through  the  absorption  bulbs.  The  bubbles  should  pass  through  the 
bulbs  at  a  rate  not  greater  than  three  per  second.  When  the  evo- 
lution of  gas  slackens,  add  a  few  more  drops  of  acid,  but  not  enough 
to  cause  a  rapid  evolution  of  the  gas.  Proceed  in  this  way  until  all 
of  the  acid  has  been  added,  then  close  the  cock  in  the  dropping  funnel. 
Be  sure  that  the  water  is  running  through  the  condenser,  then  heat 
the  flask  with  a  low  flame,  regulating  the  heat  so  that  there  will  be 
no  rapid  evolution  of  gas.  Finally  heat  to  boiling  and  boil  for  three 
minutes.  Remove  the  burner  and  immediately  open  the  stopcock 
carefully  to  admit  air  and  prevent  the  potash  solution  from  being 
drawn  back.  Allow  the  apparatus  to  cool  for  two  or  three  minutes, 
then  connect  with  the  aspirator  and  draw  air  through  for  thirty 
minutes.  Detach  the  absorption  apparatus,  place  the  caps  on  the 
ends,  allow  it  to  stand  in  the  balance  case  for  twenty  minutes,  and 
weigh  as  before.  From  the  increase  in  weight  calculate  the  per- 
centage of  carbon  dioxide  in  the  sample. 

Notes.  —  i.  The  U-tube  for  drying  the  gas  should  be  filled  with  the 
granular  and  not  the  fused  calcium  chloride,  which  contains  calcium 
oxide  and  consequently  absorbs  carbon  dioxide.  Even  with  the 
granular  calcium  chloride  when  the  tube  is  first  filled,  a  stream  of 


AGRICULTURAL  ANALYSIS  159 

carbon  dioxide  should  be  passed  through  it  for  half  an  hour  to 
neutralize  any  lime  which  might  be  present.  The  excess  of  car- 
bon dioxide  must  be  removed  by  a  current  of  air. 

2.  Sulphuric  acid  should  not  be  used  to  dry  the  carbon  dioxide 
passing  into  the  absorption  bulbs,  because  it  dries  gases  more  thor- 
oughly than  calcium  chloride.     On  leaving  the  bulb,  the  gas  passes 
over  calcium  chloride,  therefore,  if  it  were  first  dried  by  means 
of  sulphuric  acid,  it  would  leave  the  absorption  apparatus  carrying 
more  moisture  than  when  it  entered.     The  result  would  be  a  loss  of 
water  from  the  absorption  bulb. 

3.  The  Geissler  potash  bulb  may  be  used  until  a  white  precipi- 
tate of  potassium  bicarbonate  in  the  first  bulb  shows  that  the  liquid 
is  saturated. 

4.  The  guard  tube  .//prevents  carbon  dioxide  or  moisture  passing 
back  into  the  absorption  apparatus.     It  can  be  used  for  a  large 
number  of  determinations  without  refilling. 

5.  The  above  apparatus  may  be  used  for  the  determination  of 
carbon  dioxide  in  carbonates,  baking  powder,  etc. 

Statement  of  Results  as  Oxides 

All  results  of  the  soil  analysis  should  be  calculated  as  per  cent 
of  the  soil  dried  to  constant  weight  in  the  water  oven,  and  stated 
in  the  following  order : 


Insoluble  matter    ... 
Soluble  Silica 
Potash  (K.2O) 
Soda  (Na2O) 
Lime  (CaO) 

Magnesia  (MgO)  ... 
Manganese  Oxide  (MnO) 
Ferric  Oxide  (Fe2Oa)  . 
Alumina  (Al2Os)  ... 
Phosphorus  Pentoxide 
Sulphur  Trioxide  (SO3)  . 
Carbon  Dioxide  (CO2)  . 
Volatile  matter  ... 

Total. 
Humus    . 


Also  calculate  the  following  statement  of  results 


160  QUANTITATIVE  ANALYSIS 

Statement  of  Results  as  Elements 

Insoluble  matter ) 

Soluble  Silica > 

Nitrogen 

Phosphorus 

Potassium 

Calcium 

Magnesium 

Iron 

Sulphur 

Sodium 

Aluminium 

Manganese 

Inorganic  Carbon 


Oxygen  equivalent  of  above  elements  (except  ) 


Nitrogen) 

Volatile  matter  (less  Nitrogen) 
Total   .     . 
Humus 


NOTE.  —  If  the  organic  carbon  is  added  to  the  above  list  of  determined  elements,  the 
remaining  "  volatile  matter  "  consists  chiefly  of  organic  hydrogen  and  oxygen,  combined 
water  (as  in  hydrated  silicates),  and  errors  due  to  unavoidable  changes  in  mineral  com- 
pounds during  ignition. 

REFERENCES 

SNYDER,  Soils  and  Fertilizers. 

WILEY,  Agricultural  Analysis,  Vol.  I,  Soils  (1906). 


PART  V 

STOICHIOMETRY 

EMPIRICAL   FORMULAS 

THE  Law  of  Definite  Proportions  states  that  chemically  homo- 
geneous substances  —  chemical  compounds  —  always  have  the  same 
composition.  Common  salt,  the  chloride  of  sodium,  is  always 
found  upon  analysis  to  contain  chlorine  and  sodium  in  the  same 
proportions  by  weight.  The  elements  in  any  chemical  compound 
are  always  found  in  a  certain  definite  ratio,  and  it  is  by  means  of 
this  ratio  that  we  are  often  able  to  identify  a  compound.  In  the 
case  of  silver  chloride  it  has  been  found  by  analysis  that  there  is 
24.74  per  cent  of  chlorine  and  75.26  per  cent  of  silver  ;  that  is,  in 
100  grams  of  silver  chloride  there  are  24.74  grams  of  chlorine  and 
75.26  grams  of  silver.  If  the  combining  weight  of  chlorine  is 
35.45  grams,  there  will  be  as  many  combining  weights  of  chlorine 
in  24.74  grams  of  chlorine  as  35.45  is  contained  in  24.74  which  is 
0.69.  Similarly,  if  the  combining  weight  of  silver  is  107.93  grams, 
in  75.26  grams  of  silver  there  are  0.69  combining  weights. 
Hence,  in  100  grams  of  silver  chloride  there  are  0.69  combining 
weights  of  chlorine  and  0.69  combining  weights  of  silver  ;  that  is, 
they  are  present  in  the  ratio  of  0.69  Ag  to  0.69  Cl,  or  i  :  i.  The 
simplest  formula  for  silver  chloride,  therefore,  is  AgCl,  and  is 
known  as  the  Empirical  Formula. 

In  a  similar  manner,  the  empirical  formulas  of  more  complex 
compounds  may  be  calculated.  A  substance  on  analysis  gave  the 
following  percentage  composition  : 

Pb,  68.31;  S,  10.54;   O,  21.15. 
What  is  the  empirical  formula  ? 

Pb=  =  °-330,  -*-  0.330  =1.00. 


S  =  3^06  =  °'329'  "*"  °'330  =  0<997' 

„        21.15 

=  x-  320,  •*-(>.  3  30  =4.00. 

161 


1  62  QUANTITATIVE  ANALYSIS 

The  ratio  of  the  combining  weights  as  found  above  is 
0.330  :  0.329  :  1.32.  Dividing  by  the  greatest  common  divisor  gives 
the  ratio  in  whole  numbers,  as  I  :  1:4.  The  empirical  formula, 
therefore,  is  PbSO4.  Because  of  unavoidable  errors  in  the  analysis, 
the  values  of  the  percentages  almost  always  vary  from  the  theo- 
retical value.  Although  this  makes  a  slight  variation  in  the  ratio  as 
seen  in  the  case  of  sulphur  in  the  problem  above,  the  value  is  so 
close  that  it  may  be  taken  as  unity. 

PROBLEMS 

Calculate  the  empirical  formula  from  the  percentage  composition 
of  each  of  the  following  compounds  : 

1.  Na,  34.38^  C,    14.89;  O,     47.73. 

2.  K,    16.12;  Pt,  40.10;  Cl,    43.78. 

3.  K,    26.58;  Cr,  35.37;  O,     38.02. 

4.  N,    14.32;  H,     4.11;  Mo,  32.63;    0,48.95. 

5.  C,    31.99;  H,      4.03;  O,     63.98. 

Percentage  Composition 

The  calculation  of  the  percentage  composition  of  a  substance 
from  its  empirical  formula  is  the  reverse  of  the  foregoing.  In 
magnesium  sulphate  (MgSO4),  the  molecule  is  composed  of  com- 
bining weights  of  magnesium,  sulphur,  and  oxygen  in  the  ratio 
1:1:4.  The  molecular  weight  will  then  be  the  sum  of  these  com- 
bining weights. 

Mg=  24.36 

S  =  32.06 

4  O  =  64.00 

120.42 

In  one  gram  molecule  of  magnesium  sulphate  (120.42  grams) 
there  are  24.36  grams  of  magnesium,  32.06  grams  of  sulphur,  and 
4  x  1  6  (64)  grams  of  oxygen.  Therefore, 

Per  cent 

=  o  .2023  x  100=  20.23 


120.42 

S  =  32>o6  =  0.2662  x  ioo  =  26.62 
120.42 

=  0.5315  x  100=  53.15 


I20'42  100.00 


STOICHIOMETRY  163 

In  a  similar  manner  the  percentage  of  any  combination  of  ele- 
ments may  be  calculated,  as,  for  example,  MgO  and  SO3  in  magne- 
sium sulphate. 

Per  cent 

=  33-52 


=  0.6648  X  100  = 

MgSO4     120.42 

PROBLEMS 

Calculate  the  percentages  of  the  constituents  from  the  empirical 
formulas  in  the  following  problems  : 

6.  The  empirical  formula  of  zinc  sulphate  is  ZnSO4.     Calculate 
the  percentages  of  Zn  and  ZnO. 

7.  The   empirical  formula  of   ferrous   ammonium   sulphate  is 

FeS04(NH4)2S04  •  6  H2O. 

Calculate  the  percentages  of  Fe,  FeO,  S,  SO3,  and  H2O. 

8.  The  empirical  formula  of   zinc  pyrophosphate  is  Zn2P2O7. 
Calculate  the  percentages  of  ZnO  and  P2O5. 

9.  The  empirical  formula  of  calcium  silicate  is  CaSiO3.     Calcu- 
late the  percentages  of  CaO  and  SiO2. 

GRAVIMETRIC   CALCULATIONS 

There  are  a  few  isolated  cases  in  gravimetric  analysis  in  which 
the  substance  to  be  determined  is  weighed  in  the  form  in  which 
the  result  is  to  be  expressed.  This  is  true  in  the  determination  of 
nickel,  which  is  sometimes  weighed  as  the  metal,  in  which  case  the 
percentage  is  easily  calculated. 

Weight  of  constituent  sought  x  100  =         ent        of  constituent 

Weight  of  substance  taken 

In  the  majority  of  cases  the  compound  weighed  contains  other 
elements  besides  the  one  to  be  determined,  as  in  the  determination 
of  silver,  in  which  case  the  substance  is  weighed  as  silver  chloride. 
The  amount  of  silver  present  is  calculated  from  the  percentage 
composition  of  silver  chloride. 

One  gram  molecule  of  silver  chloride  (143.38  grams)  contains 


164  QUANTITATIVE  ANALYSIS 

one  combining  weight  of  silver  (107.93  grams).     If  the  precipitate 
weighs  0.2  gram,  then  letting  x  equal  the  weight  of  silver, 

AgCl         Ag         wt.  of  ppt. 
143.38  :  107.93  :  :  0.2  gram  :  x. 
x  =  o.  1  506  gram  of  silver. 

When  barium,  barium  oxide,  or  sulphur  are  to  be  determined, 
they  can  be  weighed  in  the  form  of  barium  sulphate  and  the  con- 
stituents calculated  in  a  manner  similar  to  that  given  above.  In 
each  case,  let  x  equal  weight  of  constituent  sought. 

(a)  BaSO4  :  Ba     :  :  (wt.  of  ppt.)  :  x; 

(b)  BaSO4  :  BaO  :  :  (wt.  of  ppt)  :  x\ 

(c)  BaSO4  :  S        :  :  (wt  of  ppt.)  :  x. 

If  we  wish  to  calculate  the  potassium  chloride  in  a  precipitate 
of  potassium  chlorplatinate  (K2PtCl6),  it  is  evident  that  two  mole- 
cules of  KC1  will  be  formed  from  one  molecule  of  the  precipitate. 

K2PtCl6  :  2  KC1  :  :  (wt.  of  ppt)  :  x. 

Potassium  is  often  calculated  as  the  oxide,  and  it  is  then  necessary 
to  express  the  K2PtCl6  in  terms  of  this  compound. 

It  is  evident  that  for  potassium  the  following  relation  holds 
true: 

K2PtCl6  :  2  K  :  :  (wt  of  ppt.)  :  x  (wt.  of  K). 

Now,  two  combining  weights  of  potassium  (2  K)  form  one  mole- 
cule of  potassium  oxide  (K2O).  Consequently, 

2  K  :  K2O  :  :  x  \y  (wt  of  K2O). 
Expressing  these  proportions  in  the  form  of  equations,  we  have: 

K2PtClfi  =  wt.  of  ppt.  . 
2  K        x  (wt  of  K)  ' 

2K      ^(wt.  of  K) 


K20     y  (wt  of  K20) 
Multiplying  the  two  equations, 

K2PtCl6       2K  =wt.  of  ppt.         x  (wt.  of  K) 
2  K          K2O     x  (wt.  of  K)     y  (wt.  of  K2O)* 


STO1CH1OMETRY  165 

Canceling,  we  have, 

K2PtCl6  =    wt.  of  ppt. 
K2O    ~^/(wt.  of  K2O)' 

Expressing  as  a  proportion, 

K2PtCl6  :  K2O  :  :  wt.  of  ppt.  :  y  (wt.  of  K2O). 

Or,  since  in  K2PtCl6  there  are  two  combining  weights  of  potas- 
sium, K,  we  have  enough  to  make  two  molecules  of  KC1  or  one 
molecule  of  K2O.  Therefore 

K2PtCl6=K20. 
Hence  K2PtCl6  :  K2O  :  :  wt.  of  ppt. :  wt.  of  K2O. 

Factors 

The  amount  of  the  constituent  in  the  substance  weighed  is  often 
determined  by  means  of  factors.  In  the  foregoing  examples  the 
sulphur  in  barium  sulphate  was  calculated  by  the  expression 

BaSO4  :      S      :  :  (wt.  of  ppt.)  :  x  (wt.  of  S  present). 
233.5    :   32-06  :  :  (wt  of  ppt.)  :  x 

Solving  for  x  we  have  : 

12  O6 

x  ==  -^— - —  x  (wt.  of  the  precipitate). 
233-5 

It  is  evident  that  the  value -^°—  =  0.1373,  which  represents  the 

amount  of  sulphur  equivalent  to  one  gram  of  barium  sulphate,  is 
a  constant  quantity.  Therefore,  the  sulphur  in  any  quantity  of 
barium  sulphate  may  be  determined  by  multiplying  its  weight  by 
this  value,  which  is  called  the  factor  for  the  conversion  of  barium 
sulphate  to  sulphur. 

Other  factors  may  be  similarly  calculated. 

Barium  oxide  in  barium  sulphate  : 

BaSO4  :  BaO  :  :  wt.  of  ppt.  :  x. 
—  BaO     x(wt   of  pptjB 


BaSO4 


1  66  QUANTITATIVE  ANALYSIS 


Potassium  in  potassium  chlorplatinate  : 

K2PtCl6  :  2  K  :  :  wt.  of  ppt.  :  x. 


Potassium  oxide  from  the  potassium  chlorplatinate  : 
K2PtCl6  :  K2O  :  :  wt.  of  ppt.  :  x. 

1941,  factor. 


K2PtCl6        485.8 

From  these  calculations  it  will  be  readily  seen  that  the  factor  may 
be  considered  as  the  weight  of  the  constituent  sought  in  one  gram 
of  the  substance. 

PROBLEMS 

10.  Calculate  the  factors  for  the  following  substances: 

a.  FeO  in  Fe2O3. 

b.  P2O5  and  P    in  Mg2P2O7. 

c.  ZnO  in  ZnNH4PO4. 

d.  SO2  in  PbSO4. 

e.  PbO  in  PbSO4. 

f.  MnO2  from  Mn3O4. 

11.  What  is  the  weight  of   calcium  oxide  in   1.25   grams  of 
CaC204? 

12.  What   weight   of  pyrite  (FeS2)  must  be  taken  to  furnish 
enough  sulphur  to  make  1.6  grams  of  barium  sulphate  ? 

13.  A  substance  containing  15  per  cent  MgO,  on  being  analyzed 
gave  0.2240  gram  of  magnesium  pyrophosphate.     How  much  of 
the  sample  was  weighed  out  for  the  analysis  ? 

14.  What  weight  of  magnesium  ammonium  phosphate  will  yield 
on  ignition  0.5  gram  of  magnesium  pyrophosphate? 

2  MgNH4PO4  =  Mg2P2O7  +  2  NH3  +  H2O. 

15.  1.2  grams  of  an  alloy  containing  80  per  cent  silver  and  20 
per  cent  copper  are  dissolved  in  nitric  acid.     To  the  solution  0.3 


STOICHIOMETRY  167 

gram  of  pure  dry  potassium  chloride  is  added.     What  percentage 
of  the  silver  remains  in  solution  ? 

1 6.  A  sample  of  0.3  gram  of  bauxite  (AIO(OH))  gave  a  precipi- 
tate equivalent  to  0.25  gram  of  aluminium  oxide.     Calculate  the 
percentage  purity  of  the  bauxite. 

1 7.  The  zinc  in  2.5  grams  of  a  sample  of  zinc  ore  was  precipitated 
as  the  carbonate.     On  being  ignited  to  constant  weight  the  precipi- 
tate lost  0.2  gram  of  CO2. 

ZnCO3  =  ZnO  +  CO2. 

Calculate  the  percentage  of  zinc  in  the  sample. 

1 8.  One  gram  of  a  sample  of  rock  on  analysis  gave  0.15  gram 
of  the  mixed  chlorides  of  sodium  and  potassium.     The  potassium 
was  precipitated  as  the  potassium  chlorplatinate  (K2PtCl6),  a  pre- 
cipitate of  0.120  gram  being  obtained.     Calculate  the  percentages 
of  sodium  and  potassium  in  the  sample. 

Indirect  Methods 

In  a  solution  containing  the  chlorides  of  sodium  and  potassium 
the  amount  of  each  salt  may  be  determined  by  evaporating  the 
solution  to  dryness,  weighing  the  mixed  chlorides,  dissolving  them 
in  water,  and  determining  the  total  chlorine  present  as  silver  chlo- 
ride. This  is  a  type  of  the  class  of  indirect  methods.  The  data  are 
best  calculated  algebraically,  the  method  being  illustrated  by  the 
following  example. 

The  weight  of  the  mixed  chlorides  of  sodium  and  potassium  is 
0.3  gram,  and  the  weight  of  the  silver  chloride  is  0.6323  gram.  Cal- 
culate the  weights  of  sodium  chloride  and  potassium  chloride  in 
the  mixture. 

Let  x  =  wt.  of  KC1 ; 

Then,  (0.3  -x)  =  wt.  of  NaCl. 

(The  weight  of  AgCl  from  x)  -f  (weight  of  AgCl  from  (0.3  —  x)) 
=  0.6323  gram. 

AgCl  :  KC1  :  :  (AgCl  from  x)  :  x. 
Therefore,  (AgCl  from  x)  =  4^r  x 


168  QUANTITATIVE  ANALYSIS 

AgCl  :  NaCl  :  :  (AgCl  from  (0.3-*))  :  (0.3-*). 

Therefore,  AgCl  from  (0.3  -  x)  =  A|g|  (0.3  -x). 


.3-*)=  0.6323  gram. 


1.922  x  +  2.451  (0.3  -  x}  =  0.6323. 

—  0.529^-   =  —  0.1030. 

x   =  0.1946,  wt.  of  KC1. 
(0.3  —  x)  =  0.1054,  wt.  of  NaCl. 

A  mixture  of  BaCO3  and  CaCO3  weighed  a  grams.  On  conver- 
sion to  the  sulphates  a  weight  of  b  grams  was  obtained.  Calculate 
the  weights  of  BaO  and  CaO  in  the  original  mixture. 

Let  x  =  wt.  of  BaO. 
y  =  wt.  of  CaO. 

BaCO3         CaCO3 

-B^^-CEO8'-" 

BaSO4         CaSO4 
--- 


19740  100.10 

153.40          56.10  •* 


£3346  . 

153.40  56.10    ' 

The  equations  are  then  solved  for  the  values  of  x  and  y  as  shown 
in  the  last  problem. 

PROBLEMS 

19.  A  mixture   of   the   carbonates  of  calcium    and  magnesium 
weighs  1.2  grams.     The  carbon  dioxide  obtained  from  this  mixture 
weighs  0.58  gram.     Calculate  the  weights  of  calcium  and  magne- 
sium. 

20.  In  a  mixture  of  2.3  grams  of  the  sulphates  of  lead  and  barium 
there  is  0.675  gram  of  SO3.     Calculate  the  weights  of  PbO  and 
BaO  present. 


STOICHIOMETRY  169 

21.  A  mixture  of  bromide  and  chloride  of  silver  weighs  4  grams. 
The  bromine  is  replaced  by  chlorine,  and  the  mixture  then  weighs 
3.8  grams.  What  is  the  percentage  of  bromine  present? 

The  Volume  of  a  Reagent  Necessary  for  a  Given  Reaction 

The  amount  of  a  reagent  necessary  to  bring  about  a  given 
reaction  must  often  be  calculated.  The  following  examples  are 
types  of  this  class  of  calculations. 

How  many  cubic  centimeters  of  a  barium  chloride  solution  con- 
taining 50  grams  of  the  crystallized  salt  (BaCl2  •  2H2O)  per  liter 
will  be  necessary  to  completely  precipitate  the  sulphuric  acid  in  a 
solution  containing  0.25  gram  of  potassium  sulphate  ? 

From  the  equation, 

K2SO4+  BaCl2  -  2  H2O  =  BaSO4  +  2  KC1  +  2  H2O, 

it   is  evident  that  one  gram   molecule  of  barium  chloride  (244.3 
grams)  is  equivalent  to  one  gram  molecule  of  potassium  sulphate 
(174.4  grams). 
Then, 

K2SO4      BaCl2  •  2H2O        wt.  of  K2SO4        wt.  of  BaCl2  *  2  H2O 
174.4      :        244.3          '>'.  0.25  :  x. 

^=0.3501  gram  of  BaCl2  •  2  H2O  necessary  to  precipitate  the 
sulphate. 

i  c.c.  barium  chloride  solution  =  0.05  gram  BaCl2-  2  H2O. 
0.3501 


0.05 


=  7  c.c.  of  the  solution. 


The  other  type  of  problem  involves  the  use  of  the  specific  gravity 
of  the  solution  used. 

c       .,,  .,.  Weight  of  volume  of  liquid 

Specific  gravity  =  „,  .  , — s ^   — - — - 

Weight  of  same  volume  of  standard 

This  ratio  gives  the  number  of  times  the  liquid  is  heavier  than  the 
same  volume  of  the  standard.  The  standard  which  is  used  is  the 
weight  of  one  cubic  centimeter  of  water  at  its  greatest  density,  4°  C. 
Therefore, 

0       .,,  Weight  of  I  c.c.  liquid 

Specific  gravity  =  ...  .  , — —. —  —  • 

J      Weight  of  i  c.c.  water 


I/O  QUANTITATIVE  ANALYSIS 

And  since  the  weight  of  one  cubic  centimeter  of  water  is  one 
gram,  we  have 

c       .,,  Weight  of  i  c.c.  liquid 

Specific  gravity  = — , 

i  gram 

or 

Specific  gravity  =  Weight  of  i  c.c.  of  the  liquid. 

In  determining  the  specific  gravity  it  is  not  always  convenient 
to  measure  the  volume  of  substances  at  4°  C.,  but  at  more  conven- 
ient temperatures,  such  as  15°  or  20°.  The  value  of  the  specific 
gravity  is  expressed  in  terms  of  the  standard  at  4°  C.  and  is  written 
i5°/4°,  which  signifies  that  the  substance  was  measured  at  1 5°  and 
compared  with  water  at  4°,  i.e.,  the  ratio  of  weights  of  equal 
volumes  of  the  liquid  at  15°  and  of  the  standard  at  4°;  4°/4°  signifies 
that  the  weight  of  equal  volumes  are  compared  at  the  same  tem- 
perature, <£ ;  likewise,  2O°/2O°  signifies  the  temperature  was  20° 
when  the  ^eights  were  compared. 

How  many  cubic  centimeters  of  hydrochloric  acid  (sp.  gr.  1.04) 
containing  8.16  per  cent  of  HC1  are  necessary  to  completely  pre- 
cipitate the  silver  from  i .  5  grams  of  silver  sulphate  ? 

Ag2S04  +  2  HC1  =  2  AgCl  +  H2S04. 

From  this  equation  it  is  evident  that  one  gram  molecule(3 1 1 .9  grams) 
of  silver  sulphate  is  precipitated  by  two  gram  molecules  (72.92 
grams)  of  hydrochloric  acid,  and  the  amount  of  the  acid  necessary 
to  precipitate  the  silver  in  1.5  grams  of  silver  sulphate  would  be 

Ag2SO4    2HC1          wt.  of  AgSO4      wt.  of  HC1 
311.9  :   72.92       ::  1.5  :  x. 

#=0.3506  gram  HC1  necessary  to  precipitate  the  silver. 

i  c.c.  of  HC1  (sp.  gr.  i. 04)  =  1.04  grams. 
It  contains  8.16  per  cent  HC1  by  weight. 
Therefore, 

i  c.c.  of  HC1  =(0.0816  x  1.04)  gram  HC1 
=0.0849  gram  HC1. 

To  furnish  0.3506  gram  HC1, 
0-35Q6 


STOICHIOMETRY  171 

Therefore,  4.13  c.c.  of  the  solution  will  be  required  to  precipitate 
the  silver. 

PROBLEMS 

22.  How  many  cubic  centimeters  of  silver  nitrate  solution  (100 
grams  of  AgNO3  per  liter)  will  be  necessary  to  completely  pre- 
cipitate the  chlorine  from  0.22  gram  of  BaCl2  •  2H2O? 

23.  How  many  cubic  centimeters  of  sodium  ammonium  hydrogen 
phosphate  solution  (microcosmic  salt,  NaNH4HPO4  •  4 H2O)  con- 
taining 1 5  grams  of  the  salt  per  liter  will  be  necessary  to  precipitate 
the  magnesium  from  1.2  grams  of  a  substance  containing  40  per 
cent  magnesium  oxide? 

24.  A  sample  of  i  gram  of  barium  carbonate,  the  only  impurity 
in  which  is  3.5  per  cent  SiO2,  is  dissolved  in  hydrochloric  acid. 
How  many  cubic  centimeters  of  sulphuric  acid  solution  (sp.  gr. 
1. 1  o)  containing   14.35  percent  H2SO4  by  weight  v  M   be  neces- 
sary to  completely  precipitate  the  barium  as  barium  sulphate  ? 

25.  How  many  cubic  centimeters  of  ammonium  hydroxide  (sp- 
gr.  0.96),  containing  9.91   per  cent  NH3,  would  be  necessary  to 
completely  precipitate  the  iron  in  a  solution  containing  1.3  grams 
of  ferric  chloride  ? 

VOLUMETRIC   CALCULATIONS 
ACIDIMETRY   AND    ALKALIMETRY 

A  normal  acid  solution  contains  one  combining  weight,  or  1.008 
grams  of  replaceable  hydrogen,  in  one  true  liter.  One  combining 
weight  of  hydrogen  is  furnished  by  one  gram  molecule  of  hydro- 
chloric acid ;  hence,  it  is  necessary  to  have  one  gram  molecule  of 
hydrochloric  acid,  i.e.,  the  molecular  weight  in  grams  (36.46)  dis- 
solved in  one  liter,  to  have  contained  therein  1.008  grams  of 
hydrogen.  One  gram  molecule  of  sulphuric  acid,  H2SO4,  contains 
two  combining  weights  of  hydrogen,  or  2.016  grams.  Hence,  to 
obtain  1.008  grams  per  liter,  one  gram  molecule  of  sulphuric  acid 
would  have  to  be  contained  in  two  liters,  or  one-half  of  it  in  one 
liter ;  therefore,  two  liters  of  a  normal  solution  can  be  made  from 
one  gram  molecule  of  sulphuric  acid.  According  to  the  equation 

HC1  +  KOH  =  KC1  +  H2O, 

I  gram  mol.  of  HC1  (36.46  grams) 

=  I  gram  mol.  of  KOH  (56.16  grams). 


172  QUANTITATIVE  ANALYSIS 

Since, 

1000  c.c.  normal  hydrochloric  acid  solution  =  36.46  grams  HC1, 
1000  c.c.  normal  HC1  =  56.16  grams  of  KOH. 

If  56.16  grams  of  potassium  hydroxide  are  dissolved  and  made 
up  to  one  liter,  we  have  one  liter  of  a  normal  potassium  hydroxide 
solution.  Hence, 

1000  c.c.  N.  KOH  =  56.16  grams  of  KOH. 
Therefore,   1000  c.c.   N.  HC1=  1000  c.c.  N.  KOH, 
or,  i  c.c.  N.  HC1=  i  c.c.  N.  KOH. 

From  the  equation 

H2SO4  +  2  NaOH  =  Na2SO4  +  2  H2O, 

one  gram  molecule  of  sulphuric  acid  neutralizes  two  gram  molecules 
of  sodium  hydroxide. 

That  is, 
i  gram  molecule  of  H2SO4  =  2  gram  molecules  of  sodium  hydroxide, 

(98.08  grams)  (2  x  40.06  grams) 

but,  i  gram  molecule  of  H2SO4  =  2000  c.c.  N.  H2SO4, 

(98.08  grams) 
hence,  2000  c.c.       N.  H2SO4  =  2  gram  molecules  of  NaOH, 

(2  x  40.06  grams) 
or,  looo  c.c.  N.  H2SO4=  i  gram  molecule  of  NaOH. 

(40.06  grams) 

If  40.06  grams  of  sodium  hydroxide  are  dissolved  and  made  up 
to  1000  c.c.,  we  shall  have  one  liter  of  a  normal  sodium  hydroxide 
solution.  Hence, 

1000  c.c.  N.  NaOH  =  40.06  grams  NaOH. 
Therefore, 

1000  c.c.  N.  NaOH  =  1000  c.c.  N.  H2SO4, 
or, 

i  c.c.  N.  NaOH  =  i  c.c.  N.  H2SO4. 

It,  therefore,  follows  that 

i  c.c.  N.  HC1  =  i  c.c.  N.  H2SO4, 
i  c.c.  N.  KOH  =  i  c.c.  N.  NaOH, 
i  c.c.  N.  HC1  =  i  c.c.  N.  NaOH, 
i  c.c.  N.  H2SO4  =  i  c.c.  N.  KOH, 


STOICHIOMETRY  173 

or,  in  general,  one  cubic  centimeter  of  any  normal  acid  solution  is 
equivalent  to  one  cubic  centimeter  of  any  normal  alkali  solution,  or 
normal  solutions  of  acids  and  alkalies  are  equal,  cubic  centimeter  for 
cubic  centimeter. 

The  following  typical  exercises  will  emphasize  these  fundamen- 
tal principles  and  illustrate  the  relations  between  the  volumetric 
solutions  employed  in  acidimetry  and  alkalimetry,  as  well  as  the 
methods  of  calculation  : 

9.2637  grams  of  a  sample  of  KOH  were  dissolved  in  250  c.c.  of 
water;  of  this  solution  25.45  c-c-  were  equivalent  to  14.90  c.c.  of 
N.  acid.     Calculate  the  percentage  of  KOH. 
Since, 

25.45  c.c.  KOH  solution  =  14.90  c.c.  N.  acid, 

i  c.c.  KOH  solution  =14^°.=  0.5855  c.c.  N.acid, 

25-45 

and        250  c.c.  KOH  solution  =  250  x  0.5855  =  146.37  c.c.  N.acid. 

HC1  +  KOH  =  KC1  +  H2O. 
From  which  it  follows  that 

1000  c.c.  N.  HC1  =  56.16  grams  KOH. 
Hence, 
looo  c.c.  N.  HC1:  56.16  grams  KOH 

:  :  146.37  c.c.  N.  acid  \x  grams  KOH. 


Solving,  x  =  56.16  x  146.37  =  8 


220  grams 

IOOO 

Hence,  8.220  grams  of  KOH  were  furnished  by  9.2637  grams  of 
the  sample.  What  percentage  of  the  sample  is  pure  potassium 
hydroxide  ? 

grams  sample     grams  KOH 

9.2637         :         8.220        ::  100  per  cent  :  x  per  cent. 
Solving, 

8.220  x  loo 


9.2637 


=  gg  Therefore,  88.73  per  cent. 


This  same  result  may  be  obtained  by  rinding  the  relation  of  the 
alkali  in  terms  of  the  normal  acid.     It  is  sometimes  preferable  to 


174  QUANTITATIVE  ANALYSIS 

express  the  relation  of  the  solutions  in  terms  of  the  standard 
solution. 

14.90  c.c.  N.  acid  =  25.45  c-c-  KOH  solution. 

i  c.c.  N.  acid  =  1.708  c.c.  KOH  solution. 
Since  1000  c.c.  N.  acid  =  56.16  grams  KOH, 

i  c.c.  N.  acid  =  0.05616  gram  KOH, 
then, 

1.708  c.c.  KOH  solution  =  0.05616  gram  KOH. 
Hence, 
1.708  c.c.  KOH  solution  :  0.05616  gram  KOH 

: :  250  c.c.  KOH  solution  :  x  grams  KOH. 

Solving,         x  =  °-°56i6  x  250  =  ^2Q  gmms  KQH 
1.708 

The  percentage  is  found  as  above. 

50  c.c.  of  a  sample  of  nitric  acid  of  a  specific  gravity  1.176  were 
diluted  to  250  c.c.  Of  this  solution  33.10  c.c.  were  neutralized  by 
35.55  c.c.  of  N.  KOH.  Calculate  the  percentage  of  nitric  acid  in 
the  sample. 

33.10  c.c.  HNO3  solution  =  35.55  c.c.  N.  KOH, 
i  c.c.  HNO3  solution  =  1.074  c.c.  N.  KOH, 
then,  250  c.c.  HNO3  solution  =  268.50  c.c.  N.  KOH. 

Since,  HNO3  +  KOH  =  KNO3  +  H2O, 

1000  c.c.  N.KOH  =  1000  c.c.  N.HNO3  =  63.02  grams  HNO3. 
Therefore, 
looo  c.c.  N.KOH  :  63.02  grams  HNO3 

: :  268.50  c.c.  N.KOH  \x  grams  HNO3. 
Solving,         *  =  63.02  x  268.50  =  I6       grams  HNQ 

IOOO 

The  specific  gravity  of  the  nitric  acid  is  1.176,  i.e.,  i  c.c.  weighs 
1.176  grams,  then  50  c.c.  will  weigh  50  x  1.176  or  58.80  grams, 
which  is  the  weight  of  the  sample  employed  in  the  analysis. 


STOICHIOMETRY  175 

Therefore, 

58.80  grams  sample  :  16.92  grams  HNO3 

: :  loo  per  cent  \x  per  cent  HNO3. 


Therefore,  28.78  per  cent  of  HNO3  in  the  sample. 

A  sample  of  corn  weighing  2.0894  grams  was  taken  for  analysis 
and  the  nitrogen  determined  by  the  Kjeldahl  process  with  the 
following  results :  30.00  C:C.  of  N/3  acid  (HC1)  were  placed  in  the 
receiving  flask  and  after  distillation  22.39  c-c-  of  a  standard  am- 
monium hydroxide  solution  (i.o  c.c.  =  1.004  c>c-  N/3  acid)  were 
required  to  neutralize  the  excess  of  acid.  Calculate  the  percent- 
age of  nitrogen  and  the  percentage  of  total  proteids.  Proteids  are 
6.25  times  the  nitrogen.  If 

i.o  c.c.  NH4OH  solution  =  1.004  c'c-  N/3  acid, 
then, 

22.39  c.c.  NH4OH  solution  =  22.39  x  1.004  =  22.48  c.c.  N/3  acid; 

therefore,  there  were  22.48  c.c.  of  the  standard  N/3  acid  not  neu- 
tralized by  the  ammonia  distilled  over. 

30.00  c.c.  N/3  acid  introduced  into  the  flask, 
22.48  c.c.  N/3  acid  in  excess  in  the  flask, 
7.52  c.c.  N/3  acid  is  amount  neutralized  by  the  am- 
monia distilled  over. 

HC1  +  NH4OH  =  NH4C1  +  H2O, 

then,        1000  c.c.  N.  HC1  =  i  gram  molecule  of  NH4OH. 
But, 
I  gram  molecule  NH4OH  NH3        =  N, 

35.05  grams  =  17.03  grams  =  14.01  grams, 
therefore, 

1000  c.c.  N.  HC1  =  14.01  grams  nitrogen, 
1000  c.c.  N/3  HC1  =  lA^l.  =  4.670  grams  nitrogen, 

and  i  c.c.  N/3  HC1  =  0.004670  gram  nitrogen. 

J 


1 76  QUANTITATIVE  ANALYSIS 

Then, 

7.52  c.c.  N/3  acid  =  0.004670  x  7.52  =  0.03512  gram    nitrogen, 
and  the  percentage  this  is  of  the  original  sample  is  found  by  the 
following  proportion : 
2.0894  grams  sample  :  0.03512  gram  nitrogen 

:  :  100  per  cent :  x  per  cent. 

Solving,  ^0.03512  x  ioo=  l6S         cent 

2.0894 

Therefore,   1.68  per  cent  of  nitrogen  in  the  sample,  and  6.25  x 
1.68  =  10.50  per  cent  of  total  proteids.   . 

A  sample  of  calcium  carbonate  weighing  0.6759  gram  was  dis- 
solved in  44.50  c.c.  of  1.005  N/2  acid  (HC1),  and  the  excess  of  acid 
neutralized  by  18.21  c.c.  of  a  standard  alkali,  i.oo  c.c.  of  the  acid 
being  equal  to  1.031  c.c.  of  the  alkali.  Calculate  the  purity  of  the 
calcium  carbonate. 

1.031  c.c.  of  the  alkali  =  i  c.c.  of  acid, 

T  Q   o  r 

and       1 8. 2 1  c.c.  of  the  alkali  =  — -—  =  17.66  c.c.  acid. 

1.031 

44.50  c.c.  of  1.005  N/2  acid  used 

17.66  c.c.  of  1.005  N/2  acid  remaining 

26.84  c-c-  of  i  -°°5  N/2  acid  used  in  neutralizing  the  CaCO3. 

Since   the  acid  is  1.005  times  as  strong  as  N/2  acid,  26.84  c-c« 
will  equal  26.84  x  1-005  =  26.97  c-c-  N/2  acid. 

CaCO3  +  2  HC1  =  CaCl2  +  CO2  +  H2O. 

i  gram  molecule  of  CaCO3,  i.e.  (100.1  grams)  =  2000  c.c.  N.  HC1  = 
4000  c.c.  N/2  HC1. 

Therefore, 

4000  c.c.  N/2  HC1 :  100.1  grams  CaCO3 

: :  26.97  c.c.  N/2  HC1  \x  grams  CaCO3. 

Solving,        x  =  IQQ.i  x  26.97  =  0>6750  gram  CaC03. 

4000 
Then, 

0.6759  gram  of  sample  :  0.6750  gram  CaCO3 

: :  100  per  cent :  x  per  cent. 


UNIVERSITY   ) 

STOICHIOMETR  Y  1 77 


Solving,  ^  =  0.6750x100 

0.6759 

Therefore,  99.87  per  cent  of  the  sample  is  CaCO3. 

PROBLEMS 

26.  11.2798   grams  of  NaOH  were   dissolved    and    diluted   to 
250  c.c.,  36.15  c.c.  of  which  were  equivalent  to  37.40  c.c.  N.  acid. 
Calculate  the  percentage  purity. 

27.  6.5563  grams  of  NaKCO3  were  dissolved  and  diluted  to  250 
c.c.,  42.88  c.c.  of  which  were  equivalent  to  17.71   c.c.  of  N.  acid. 
Calculate  the  percentage  purity. 

28.  0.7752  gram  of  calcium  carbonate  was  dissolved  in  32.00 
c.c.  N.  acid;  the  excess  of  acid  required  16.52  c.c.  N.  KOH  for 
neutralization.     Calculate  the  percentage  purity  of  the  calcium 
carbonate. 

29.  9.4116  grams  of  a  mixture  of  sodium  hydroxide  and  sodium 
carbonate  were  dissolved  and  made  up_to  250  c.c.  ;  40.85  c.c.  of 
this  solution  required  24.32  c.c.  N.  acid  when  phenolphthalein  was 
used  as  an  indicator,  and  30.56  c.c.  when  methyl  orange  was  used. 
Calculate  the  percentages  of  sodium  carbonate  and  sodium  hydrox- 
ide.    Calculate   the  percentage  of   total   alkalinity  expressed   as 
sodium  oxide. 

30.  24.84  c.c.  NH4OH,  the  specific  gravity  of  which  was  0.944, 
were  diluted  to  250  c.c.,  and  28.50  c.c.  were  equivalent  to  22.71  c.c. 
N.  acid.     Calculate  the  percentage  of  ammonia  in  the  sample. 

31.  15.00  c.c.  of  H2SO4  solution,  the  specific  gravity  of  which 
was  1.624,  were  diluted  to  250  c.c.,  and  25.55  c.c.  of  this  solution 
were  equivalent  to  35.25  c.c.  of  N.  KOH.     Calculate  the  percent- 
age of  acid  in  the  sample. 

32.  25  c.c.   of  a  sample  of  HC1,  the  specific  gravity  of  which 
was  1.116,  were  diluted  to  250  c.c.  ;  20.54  c-c-  °f  this  solution  were 
equivalent  to    14.30  c.c.   N.  KOH.     Calculate  the  percentage  of 
HC1  in  the  sample. 

33.  23.12  c.c.  of    HNO3  solution,    specific  gravity   1.19,  were 
diluted  to  250  c.c. ;  25.00  c.c.  of  this  solution  were  equivalent  to 
12.92  c.c.  N.  KOH.     Calculate  the  percentage  of  nitric  acid  in  the 
sample. 


QUANTITATIVE  ANALYSIS 

34.  How  many  cubic  centimeters  of  0.9  N.  H2SO4  solution  are 
required  to  precipitate  the  barium  from  0.25  gram  BaCl  •  2  H2O  ? 

35.  In  the  absorption  method  for  standardizing  the  KOH  solu- 
tion 7.9284  grams  HC1  gas  were  absorbed  and  diluted  to  250  c.c. ; 
24.89  c.c.  of  this  solution  were  equivalent  to  21.65  c-c-  of  the  KOH 
solution.     Calculate  the  normality  of  the  KOH  solution. 

36.  25.00  c.c.  of  a  standard  acid  were  diluted  to  250  c.c.  and  25 
c.c.  of  this  solution  were  treated  with  AgNO3.     The  silver  chloride 
from  the  same  weighed  0.3505  gram.     What  was  the  normality  of 
the  standard  acid  ? 

37.  A  solution  of  KOH  requires  27.00  c.c.  of  a  standard  HC1 
(i  c.c.  of  which  =  0.022  gram  CaCO3)  for  neutralization.     What  is 
the  weight  of  potassium  hydroxide  in  the  solution  ? 

38.  One  gram  of  silver  is  dissolved  in  nitric  acid.     To  the  solu- 
tion 8  c.c.  of  N.  HC1  are  added.     What  percentage  of  the  silver 
remains  in  solution  ? 

OXIDATION  AND  REDUCTION 
Balancing  Equations 

In  writing  the  equations  representing  oxidations  and  reductions, 
considerable  difficulty  is  experienced  owing  largely  to  the  fact  that 
the  elements  undergo  a  change  of  valency.  These  equations  can 
be  balanced  only  when  all  of  the  reacting  substances  and  products 
are  known.  The  numerical  values  can  be  readily  obtained  and  the 
reactions  more  easily  understood  if  they  are  represented  as  taking 
place  by  stages,  the  final  result  being  expressed  as  the  sum  of  the 
various  steps.  A  few  specific  examples  will  illustrate  the  method 
by  means  of  which  the  equation  may  be  readily  balanced. 

If  the  reacting  substances  are  nitric  acid  and  metallic  copper, 
the  products  of  the  reaction  will  be  copper  nitrate,  nitric  oxide,  and 
water.  The  usual  action  of  an  acid  on  a  metal  is  attended  with 
the  evolution  of  hydrogen, 

Cu  +  2  HNO3  =  Cu(NO3)2  +  H2, 

which  in  the  presence  of  nitric  acid  will  be  oxidized.     The  nitric 
acid  may  be  assumed  to  break  up  as  follows : 

2  HNO3  =  H20  +  2  NO  +  3  O, 


STOICHIOMETRY  179 

and  the  hydrogen  oxidized  by  the  oxygen, 
3  H2  +  3  O  =  3  H20. 

The  first  equation  must  be  multiplied  by  three  in  order  to  provide 
enough  hydrogen  to  combine  with  the  oxygen  from  two  molecules 
of  nitric  acid.  Multiplying  by  three  and  collecting  the  equations 
we  have, 

3  Cu  +  6  HN03  =  3  Cu(N03)2  + 

2  HNO3  =  H2O  +  2  NO  + 


3  Cu  +  8  HN03  =  3  Cu(N03)2  +  2  NO  +  4  H2O. 

Adding  and  simplifying  gives  the  above. 

In  the  oxidation  of  ferrous  chloride  by  potassium  dichromate  in 
the  presence  of  hydrochloric  acid,  the  products  of  the  reaction  are 
ferric  chloride,  chromic  chloride,  potassium  chloride,  and  water. 
The  potassium  dichromate  may  be  conceived  as  splitting  up  in  the 
following  manner  : 

K2Cr207  =  K2O  +  Cr203  +  30. 
The  oxides  react  with  hydrochloric  acid, 

K20  +  2  HC1  =  2  KC1  +  H20, 
Cr203  +  6  HC1  =  2  CrCl3  +  3  H2O. 

The  oxygen  and  hydrochloric  acid  react  with  the  liberation  of 
chlorine, 


The  chlorine  reacts  with  ferrous  chloride,  oxidizing  it  to   ferric 
chloride, 

6FeCl2  +  6Cl  =  6FeCl3. 

Adding  and  simplifying  we  have  : 

K2Cr207  =  j^O  +  <>atf8 
+  2  HC1  =  2  KC1  +  H20 
+  6  HC1  =  2  CrCl3  +  3  H2O 


6  FeCl2  +  ££1  =  6  FeCl3 

K2Cr207  +  14  HC1  +  6  FeCl2  =  2  KC1  +  2  CrCl3  +  6 FeCl3  +  7  H2O, 


i8o  QUANTITATIVE  ANALYSIS 

The  reduction  of  potassium  permanganate  by  potassium  iodide 
(hydriodic  acid)  in  the  presence  of  sulphuric  acid  may  be  illus- 
trated in  a  similar  manner. 

The  potassium  permanganate  may  be  conceived  as  breaking  down 
in  the  following  manner  : 

2  KMnO4  =  K2O  +  2  MnO  +  5  O. 
The  oxides  react  with  sulphuric  acid,  forming  salts, 

K2O  +  H2SO4  =  K2SO4  +  H2O  ; 
2  MnO  +  2  H2SO4  =  2  MnSO4  +  2  H2O.  , 

The  oxygen  reacts  with  the  hydriodic  acid, 

10  KI  +  5  H2SO4  =  10  HI  +  5  K2SO4; 


Adding  and  simplifying  we  have  : 

2  KMnO4  +  10  KI  +  8  H2SO4  =  2  MnSO4  -f  6  K2SO4  +  5  12  4-  8  H2O. 

The  oxidation  of  arsenious  oxide  by  chlorine  (iodine  or  bromine) 
is  another  example. 


As2O3  +  2  C12  +  2  H2O  =  As2O5  +  4  HC1. 

Oxidizing  Agents 

The  following  compounds  are  some  of  the  more  important  oxi- 
dizing agents  from  the  standpoint  of  analytical  chemistry.  Their 
method  of  breaking  up  when  acting  as  oxidizing  agents  is  illus- 
trated. 

12  KMnO4  =  K2O  +  2  MnO  +  5  O 
(in  acid  solution). 
T^TI/T    r\         ir  r\    ,        n/r    r\  r\ 

2  KMnO4  =  K2O  +  2  MnO2  -f  3  O 
(in  alkaline  solution). 

Potassium  dichromate.  K2Cr2O7  =  K2O  -f  Cr2O3  +  3  O. 

Potassium  chlorate.  KC1O3  =  KC1  +30 

Nitric  acid.  2  HNO3  =  H2O  +  2  NO  +  3  O. 


STOICHIOMETRY  181 

Sulphuric  acid  H2SO4  =  H2O  +  SO2  +  O. 

(hot  concentrated). 

Manganese  dioxide.  MnO2  =  MnO  +  O. 

(in  acid  solution). 

Sodium  peroxide  Na2O2  =  Na2O  +  O. 

(fusion). 

Hydrogen  peroxide.  H2O2  =  H2O  +  O. 

The  halogens  oxidize  by  decomposing  water  with  the 
Bromine.  [liberation  of  oxygen.     H2O  +  C12  =  2  HC1  +  O. 
Iodine.      J 

It  should  not  be  forgotten  that  oxidizing  agents  are  reduced  to  dif- 
ferent compounds  under  different  conditions,  as  may  be  seen  in  the 
case  of  potassium  permanganate  in  acid  and  alkaline  solutions. 

Balance  the  following  equations  : 

1 .  Fe2(SO4)3  +  H2SO4  +  Zn  =  FeSO4  +  ZnSO4  +  H2O. 

2.  KN03  +  FeCl2  +  HC1  =  KC1  +  NO  +  FeCl3  +  H2O. 

3.  KC1O3  +  FeSO4  +  H2SO4  =  KC1  +  Fe2(SO4)3  +  H2O. 

4.  K2Cr2O7  +  H2SO4  +  Zn 

=  Cr2(S04)3  +  K2S04  +  ZnS04  +  H2O. 

5.  Mn02  +  H2S04  +  H2C204  =  MnSO4  +  CO2  +  H2O. 

6.  As2O3+HNO3+H2O  =  H3AsO4+NO. 

7.  K4Fe(CN)6  +  H2S04  +  KMn04 

=  K2SO4  +  MnSO4  +  K3Fe(CN)6'+  H2O. 

8.  MnO2  +  KOH  +  KC1O3  (fusion)  =  K2MnO4  +  KC1  +  H2O. 

9.  Cr2Cl6  +  NaOH  +  NaClO3  (fusion) 

=  NaCl  +  Na2CrO4  +  H2O. 

10.  Cr2(OH)6  +  Na2O2  (fusion)  =  Na2CrO4  +  Na2O  +  H2O. 

n.  K2Cr207  +  HCl+C2H5OH  =  CrCl3-hKCH-C2H4 

12.  H2S04  +  C12H22On  =  S02  +  C02 

13.  KIO3  +  KI  +  H2SO4=K2SO4+I2 

14.  KC1O  +  HI  =  KC1  +  H2O  +  I2. 
15. 


182  QUANTITATIVE  ANALYSIS 

16.  PbO2  +  HI  =  PbI2  +  H20  +  I2. 

17.  KBr03  +  KI  +  H2S04  =  KBr  +  K2SO4  +  I2  +  H2O. 

18.  KC1O3  +  KI  +  HC1=KC1  +  H2O  +  I2. 
19-  K3Fe(CN)6  +  KI  =  K4Fe(CN)6  +  I2. 

20.  Ca(OCl)2CaCl2  +  HC1  +  KI  =  CaClg  +  KC1  +  I2  +  H2O. 


PERMANGANATE  AND  BICHROMATE  METHODS 
Numerical  Relations 

The  quantitative  relations  between  certain  oxidizable  substances 
can  be  determined  by  rinding  their  values  in  terms  of  oxygen. 
Potassium  permanganate  oxidizes  ferrous  sulphate  to  ferric  sul- 
phate. It  also  oxidizes  oxalic  acid  to  carbon  dioxide  and  water. 
What  is  the  relation  between  these  two  reducing  agents  and  what 
are  their  values  in  terms  of  oxygen  ? 

The  ferrous  sulphate  is  oxidized  to  ferric  sulphate,  this  being 
equivalent  to  oxidizing  ferrous  oxide  to  ferric  oxide. 


That  is,  one  combining  weight  of  oxygen  will  oxidize  two  mole- 
cules of  ferrous  oxide,  which  is  equivalent  to  2  FeSO4  or  2  Fe. 

Similarly,  oxalic  acid  is  oxidized  by  one  combining  weight  of 
oxygen  to  carbon  dioxide  and  water, 

H2C2O4  +  O  =  2  CO2  +  H2O. 
Therefore, 

H2C204  {2  Fe 


H2C2O4-2H2O        [2FeSO4 
or  expressing  the  relation  in  grams: 


1 6  g.  of  oxygen: 


90.03  g.  oxalic  acid  = 

126.06    g.    crystallized 
oxalic  acid  = 


1 1 1.8  g.  of  Fe 

143.8  g.  of  FeO 

303.9  g.  of  FeS04 


If  the  strength  of  a  solution  is  given  in  terms  of  either  of  these 
substances,  it  stands  in  a  simple  ratio  to  the  other  substances. 


STOICHIOMETRY  183 

If  i  c.c.  of  KMnO4  =  o.O3  gram  of  oxalic  acid,  what  is  its 
strength  in  terms  of  FeO  and  oxygen? 

H2C2O4     2  FeO 
90.03  :   148.08  ::  0.03  :  x.        x  =  0.0496  gram, 

the  value  of  i  c.c.  in  terms  of  FeO. 

H2C204      O 
90.03     :  1 6  : :  0.03  \x. 

^  =  0.005331  gram,  the  value  of  i  c.c.  of  the  permanganate  in 
terms  of  oxygen. 

In  the  case  of  potassium  dichromate,  since, 

K2Cr207  =  3O 

and  O         =2  FeO  =  2FeSO4       =2Fe 

K2Cr2O7         =3O      =6  FeO  =6FeSO4       =6Fe 

294.5  grams =48  grams  =  43 1.4  grams  =  91 1.7  grams  =33 5. 4  grams. 

QUESTIONS  ON   EQUATIONS 

Equation  I,  page  181. 

How  many  gram  molecules  of  ferric  sulphate  take  part  in  the 
reaction  ?  When  ferric  sulphate  acts  as  an  oxidizing  agent,  how 
many  grams  of  available  oxygen  are  contained  in  one  gram  mole- 
cule ?  How  many  gram  molecules  of  ferrous  sulphate  can  be  ob- 
tained by  the  action  of  one  combining  weight  of  zinc?  How  many 
grams,  by  one  gram  of  zinc  ? 

Equation  3. 

One  gram  molecule  of  potassium  chlorate  contains  how  many 
grams  of  available  oxygen?  One  gram  molecule  of  potas- 
sium chlorate  will  oxidize  how  many  grams  of  FeSO4?  Of 
FeS04(NH4)2S04-6H2O. 

Equation  5. 

How  many  gram  molecules  of  manganese  dioxide  and  oxalic 
acid  take  part  in  the  reaction  ?  Considering  the  oxalic  acid  as 
crystalline,  how  many  grams  are  equivalent  to  one  gram  of  man- 
ganese dioxide  ? 

Equation  7. 

How  many  grams  of   potassium  ferrocyanide  will  reduce  the 


1 84  QUANTITATIVE  ANALYSIS 

same  amount  of  permanganate  as  one  gram  of  hydrogen  ?    As  one 
gram  of  ferrous  sulphate  ? 

Equation  n. 

Calculate  the  weight  of  alcohol  necessary  to  reduce  two  grams 
of  K2Cr2O7.  If  the  specific  gravity  of  the  alcohol  used  is  0.8043, 
how  many  cubic  centimeters  will  be  required  ? 

Methods  of  Solving  Problems 

A  solution  of  potassium  permanganate  was  standardized  by  (a) 
pure  iron,  (b)  ferrous  ammonium  sulphate,  and  (c)  sodium  oxalate. 
In  each  case  calculate  the  number  of  grams  of  oxygen  in  one  cubic 
centimeter  of  the  permanganate  and  also  the  amount  of  iron 
equivalent  to  one  cubic  centimeter  of  the  solution. 

a.  0.1104  gram  of  electrolytic  iron  was  dissolved,  out  of  contact 
with  air,  and  required  22.30  c.c.  of  the  permanganate  solution  to 
oxidize  the  ferrous  iron  to  the  ferric  condition.    We  saw  above  that 
1 6  grams  of  oxygen  are  equal  to  in. 8  grams  of  iron,  then  i  gram 
oxygen  =  6.988  grams  of  iron;  therefore,  0.1104  gram  of  iron  will 
require 

0  1104 

=  0.01580  gram  of  oxygen. 

6.988 

Since  this  quantity  of  oxygen  is  furnished  by  22.30  c.c.  of  per- 
manganate, then, 

22.30  c.c.  KMnO4  =  0.01580  gram  oxygen. 

I  c.c.  KMnO4  =  —         —  =  0.0007085  gram  oxygen. 

Therefore,  i  c.c.  KMnO4  furnishes  0.0007085  gram  of  oxygen  for 

oxidation. 

Since  22.30  c.c.  KMnO4  =  o.  1 104  gram  iron, 

1  c.c.  KMnO4=  0.004950  gram  iron. 

b.  0.8350  gram  of  ferrous  ammonium  sulphate  was  dissolved 
and  oxidized  by  24.01  c.c.  of  the  permanganate  solution. 
Since, 

FeSO4(NH4)2SO4  •  6  H2O     Fe      wt.  of  sample     wt.  of  Fe. 
392.26  grams         :        55.9      ::     0.8350       :         x. 


STOICHIOMETRY  185 

Solving, 

fof  iron  equivalent   to  this 

x  _.  55-9  x  °-  35°  =  o.  1  190  gram  J  quantity  of  ferrous  ammo- 

Inium  sulphate. 

Now,  knowing  the  grams  of  the  iron  and  the  amount  of  perman- 
ganate solution  required  to  oxidize  it  from  the  ferrous  to  the  ferric 
condition,  the  results  can  be  calculated  in  the  manner  illustrated 
in  the  preceding  example. 

c.  1.401  grams  of  sodium  oxalate  were  dissolved  and  made  up 
to  250  c.c.  ;  26.50  c.c.  of  this  solution  were  oxidized  by  25.08  c.c. 
of  the  potassium  permanganate  solution. 

5  Na2C2O4  +  2  KMnO4  +  8  H2SO4 

=  2  MnSO4  +  5  Na2SO4  4-  K2SO4  +  10  CO2  +  8  H2O. 

26.50  c.c.  oxalate  solution  =  25.08  c.c.  KMnO4, 

i  c.c.  oxalate  solution  =  0.9464  c.c.  KMnO4, 
250  c.c.  oxalate  solution  =  236.61  c.c.  KMnO4. 

From  the  above  equation 

5Na2C204=2KMn04=50, 
or,  Na2C2O4  =  O, 

i.e.,  134.1  grams  =  16  grams  of  oxygen. 

Hence, 
134.1  grams  Na2C2O4  :  16  grams  oxygen 

:  :  1.401  grams  Na2C2O4  \x  grams  oxygen. 
Solving, 


x=-  —  -    "       =0.16716  gram  oxygen. 

Since  236.61  c.c.  of  KMnO4  furnished  0.16716  gram  of  oxygen,  one 

cubic  centimeter  would  furnish     '*   'l    =  0.0007065  gram  of  oxy- 

236.61 
gen  for  oxidizing  purposes. 

Since, 

i  gram  oxygen  =  6.988  grams  iron, 

0.0007065  gram  oxygen  =  0.0007065  x  6.988  =  0.004937  gram  iron. 
Therefore, 

I  c.c.  KMnO4  =  0.004937  gram  iron. 


1 86  QUANTITATIVE  ANALYSIS 

PROBLEMS 

39.  From  the  following  data  calculate  the  number  of  grams  of 
available  oxygen  in  one  cubic  centimeter  of  a  potassium  perman- 
ganate solution  and  also  the  number  of  cubic  centimeters  of  this 
solution  required  to  oxidize  o.io  gram  of  iron. 

a.  0.0946  gram  of   metallic   iron  required   10.78  c.c.   KMnO4 
solution. 

b.  1. 145  grams  of  ferrous  ammonium  sulphate  required  18.70  c.c. 
of  the  permanganate  solution. 

c.  1.5477  grams  of  crystallized  oxalic  acid  were  dissolved  and 
made  up  to  250  c.c. ;  25.25  c.c.  of  this  solution  were  equivalent  to 
15.76  c.c.  of  the  permanganate  solution. 

Write  the  equations  representing  the  reactions  in  each  case. 

40.  3.7613  grams  of  ammonium  oxalate((NH4)2C2O4  •  H2O)  were 
dissolved  in  water  and  made  up  to  250  c.c. ;   10.00  c.c.  of  which  were 
equal  to  20.33  c-c-  of  KMnO4  solution.     If  i  c.c.  of  the  KMnO4  is 
equivalent  to  0.000830  gram  of  oxygen,  calculate  the  percentage 
purity  of  the  sample. 

41.  Calculate  the  percentage  purity  of   KH3(C2O4)2  •  2H2O,  if 
1.1881    grams   were    dissolved    and    made   up   to   250   c.c.,    and 
25.10  c.c.  of  this  solution  were  equivalent  to  17.58  c.c.  of  KMnO4, 
I  c.c.  of  which  is  equivalent  to  0.000851  gram  of  oxygen. 

42.  1.6124  grams  of  a  substance  containing  calcium  were   dis- 
solved and  made  up  to  250  c.c.     The  calcium  was   precipitated 
from  50  c.c.  of  this  solution  as  calcium  oxalate,  washed  thoroughly, 
and  then  dissolved  in  dilute  sulphuric  acid.     This  solution  was 
then  titrated  with  a  KMnO4  solution,  I  c.c.  of  which  furnished 
0.000830  gram  of  oxygen.     55-88   c.c.  of   this    KMnO4  were  re- 
quired to  oxidize  the  oxalic  acid  liberated.     Write  equations  repre- 
senting all  of  the  reactions  and  calculate  the  percentage  of  calcium 
oxide  in  the  sample. 

43.  A  solution  of  K2Cr2O7  was  standardized  with  the  following 
results : 

(a)  0.771    gram  of  ferrous  ammonium  sulphate  required  19.80 
c.c.  of  the  K2Cr2O7  solution. 

(b)  0.430  gram  of  metallic  iron  was  dissolved  and  made  up  to 
250  c.c.;  50  c.c.  of  this  solution  required  15.45  c.c.  of  the  K2Cr2O7 
solution. 


STOICHIOMETRY  187 

Write  the  equations  representing  all  of  the  chemical  changes. 
Calculate  the  number  of  grams  of  available  oxygen  in  each  cubic 
centimeter  of  the  dichromate  solution  and  the  number  of  cubic 
centimeters  of  the  solution  equivalent  to  o.  i  gram  of  iron. 

44.  10.00  c.c.  of  hydrogen  peroxide  solution  were  diluted  to 
250  c.c.,  and  titrated  against  a  potassium  permanganate  solution. 
25.00  c.c.  of  the  diluted  peroxide  were  equivalent  to  19.71  c.c.  of 
the  permanganate,  i  c.c.  of  which  contained  0.00070  gram  of  oxy- 
gen. Calculate  the  number  of  grams  of  oxygen  furnished  by 
each  cubic  centimeter  of  the  original  peroxide  solution.  Calculate 
the  percentage  purity  of  the  hydrogen  peroxide,  assuming  the  spe- 
cific gravity  to  be  one. 

lODIMETRY 

Method  of  Solving  Problems. 

In  the  solution  of  problems  in  which  a  number  of  equations  are 
involved,  short  cuts  in  the  calculations  are  often  made  possible  by 
equating  the  values  in  such  a  way  that  the  intermediate  calcula- 
tions may  be  omitted. 

If  25  c.c.  of  a  solution  of  potassium  permanganate  (i  c.c.  = 
0.004  gram  Fe)  are  added  to  an  acid  solution  of  potassium  iodide, 
how  many  grams  of  sodium  thiosulphate  (Na2S2O3  •  5  H2O)  will  be 
oxidized  by  the  iodine  liberated  ? 

Since 

i  c.c.  KMnO4  solution  =  0.004  gram  Fe, 

25  c.c.  KMnO4  solution  =  o.ioo  gram  Fe. 

Two  combining  weights  of  iron  are  equivalent  to  one  combining 
weight  of  oxygen,  or 

2  Fe  =  O, 

and  one  of  oxygen  is  equivalent  to  two  combining  weights  of 
iodine, 

O   =  2  I. 

Two   combining  weights  of  iodine  will  oxidize  two  gram    mole- 
cules of  sodium  thiosulphate, 

2 1  =  2Na2S2O3-  5H2O; 

therefore,  2  Fe  =  2  Na2S2O3  -  5  H2O. 

That  is, 

55.9  grams  Fe  =  248.3  grams  Na2S2O3  •  5  H2O. 


188  QUANTITATIVE  ANALYSIS 

It  follows  then  that 
55.9  grams  Fe :  248.3  grams  Na2S2O3  •  5H2O 

: :  o.  100  gram  Fe :  x  grams  Na2S2O3  •  5  H2O. 
Solving, 

248.3  xo. i  _ 
55.9 

Therefore,  0.4442  gram  of  sodium  thiosulphate  will  be  oxidized 
by  the  iodine  liberated. 

This  exercise  illustrates  the  common  method  employed  in  the 
solution  of  problems  in  iodimetry.  It  is  obvious  that  the  method 
may  be  applied  to  the  solution  of  other  classes  of  problems  of  oxi- 
dation and  reduction. 

QUESTIONS    ON    EQUATIONS 

Equation  13,  page  181. 

How  many  grams  of  potassium  iodate  will  be  required  to  furnish 
one  combining  weight  of  iodine  ?     One  gram  of  iodine  ? 
Equation  15. 

How  many   gram  molecules    of  chlorine  are  liberated?     How 
many  grams  of  iodine  are  equivalent  to  the  available  oxygen  in 
one  gram  molecule  of  MnO2  ?    To  one  gram  of  chlorine  ? 
Equation  17. 

How  many  grams  of  iodine  are  equivalent  to  the  available  oxy- 
gen in   50   c.c.  of  a    solution  containing  one   gram    molecule  of 
KBrO3  in  a  liter  ?     How  many  grams  of  KBrO3  should  be  dis- 
solved in  a  liter  to  make  a  half-normal  solution  ? 
Equation  19. 

How  many  grams  of  potassium  ferricyanide  are  necessary  to 
liberate  one  combining  weight  of  iodine  ?  How  many  grams  of 
the  ferricyanide  should  be  dissolved  in  a  liter  of  water  to  make  a 
normal  solution  ? 

PROBLEMS 

45-  3-°35  grams  of  arsenious  oxide  were  dissolved  and  made  up 
to  500  c.c.  ;  25.70  c.c.  of  this  solution  were  equivalent  to  37.70 
c.c.  of  an  iodine  solution.  Calculate  the  grams  of  iodine  in  one 
cubic  centimeter  of  the  iodine  solution. 

46.  An  iodine  solution  was  found  by  titration  to  be  exactly 
equivalent  to  a  thiosulphate  solution  which  was  standardized  by  a 
standard  potassium  permanganate  solution,  according  to  Exercise 


STOICHIOMETRY  189 

XXVII,  c.  If  one  cubic  centimeter  of  the  permanganate  solution 
was  equivalent  to  0.000707  gram  of  oxygen  and  28.50  c.c.  were 
equivalent  to  26.00  c.c.  of  the  thiosulphate  solution,  calculate  the 
number  of  grams  of  iodine  in  one  cubic  centimeter  of  the  iodine 
solution.  Express  the  normality  factor  of. the  iodine  solution. 

47.  7.0799  grams  of  bleaching  powder  were  taken  for  analysis, 
dissolved  and  diluted  to  1000  c.c.      50  c.c.  of  this  solution  were 
treated  with  potassium  iodide  and  acetic  acid  and  the  iodine  liber- 
ated, titrated  against  N/io  thiosulphate  solution,  of  which  24.45 
c.c.  were  required.     Calculate  the  percentage  of  available  chlorine 
in  the  sample. 

48.  0.7697   gram  of  pyrolusite  was    treated,   as   described  in 
Exercise  XXIX,  with  concentrated  hydrochloric  acid,  and  the  lib- 
erated chlorine  passed  into  a  solution  of  potassium  iodide.     This 
solution  was  diluted  to  500  c.c.,  and  50  c.c.  of  it  titrated  against 
N/io  thiosulphate   solution   of    which    11.90  c.c.  were  required. 
Calculate  the  percentage  purity  of  the  pyrolusite. 

49.  An  iodine  solution  was  standardized  by  means  of  a  standard 
dichromate   solution  (i    c.c.  =0.000848  gram  oxygen)  according 
to    the    method    described    in    Exercise    XXVII,  d.     28.29    c.c. 
K2Cr2O7  liberated  enough  iodine  to  oxidize  30.05  c.c.  sodium  thio- 
sulphate, i  c.c.  of  which  =  1.206  c.c.  of  the  iodine  solution.     Cal- 
culate the  normality  of  the  iodine  solution. 

Factor   Weights 

In  order  to  facilitate  the  calculations, -it  is  frequently  of  value  in 
volumetric  determinations  to  so  adjust  the  weight  of  the  sample  to 
the  strength  of  the  solution  that  each  cubic  centimeter  used  in  the 
titration  will  represent  a  definite  amount  of  the  constituent. 

Suppose  a  permanganate  solution  is  standardized  and  each  cubic 
centimeter  found  to  be  equivalent  to  0.0045  gram  of  iron.  If  in 
the  analysis  0.45  gram  of  the  sample  is  weighed  out  and  22.30  c.c. 
used  in  the  titration,  the  percentage  of  iron  found  would  be 

22.30x0.0045  x  I00=  22.3  per  cent. 
0.45 

For  this  particular  weight  of  substance,  therefore,  each  cubic 
centimeter  of  the  solution  used  would  indicate  one  per  cent  of  the 
constituent  sought. 


190  QUANTITATIVE  ANALYSIS 

If  0.90  gram  of  the  sample  were  taken,  each  cubic  centimeter 
would  read  0.50  per  cent;  if  0.2250  gram,  2  per  cent;  and  so  on. 

In  gravimetric  processes,  the  weight  of  the  sample  may  also  be 
so  selected  that  each  milligram  of  the  precipitate  will  represent  a 
definite  amount  of  the  substance  sought. 

How  much  pyrite  must  be  taken  for  analysis  in  order  that  each 
milligram  of  BaSO4  shall  represent  o.  i  per  cent  of  S  ? 

i  mg.  of  BaSO4  =  0.1373  mg.  of  S. 

0.1373  mg.  of  S  is  o.i  per  cent  of  0.1373  gram. 

If  0.1373  gram  of  sample  is  taken,  therefore,  each  milligram  of 
the  precipitate  will  represent  o.  i  per  cent  of  sulphur. 

PROBLEMS 

50.  How  much  limestone  must  be  taken  for  analysis  for  each 
milligram  of  calcium  sulphate  to  represent  o.  i  per  cent  of  calcium 
oxide  ? 

51.  How  much  barite  must  be  taken  for  analysis  in  order  that 
each  milligram  of  barium  sulphate  shall  represent  0.20  per  cent  of 
BaO? 

52.  One  cubic  centimeter  of  a  solution  of  KMnO4  =  0.0075 
gram    of   oxygen.     How   many  grams    of    limestone   should   be 
weighed  out  in  order  that  when  titrating  the  calcium  as  the  oxa- 
late  each  cubic  centimeter  of  the  permanganate  solution  used  cor- 
responds to  0.5  per  cent  CaO  ? 

53.  How  much  of  a  feeding  material  must  be  taken  for  analysis 
by  the  Kjeldahl  method  in  order  that  each  cubic  centimeter  of 
N/4  HC1  used  to  titrate  the  ammonia  distilled  over  shall  represent 
0.5  per  cent  of  proteid  matter.     Use  6.25  for  conversion  of  nitro- 
gen to  proteid  matter. 

MISCELLANEOUS    PROBLEMS 

54.  A  mixture  of  the  sulphates  of  sodium  and  potassium  weighs 
i.i  grams.     It  is  dissolved  in  water  and  barium  chloride  solution 
added,  a  precipitate  of  BaSO4  weighing  1.699  grams  being  obtained. 
Calculate  the  weight  of  each  sulphate  in  the  original  mixture. 

55.  How  many  grams  of  a  sample  of  fertilizer  should  be  taken 
for  analysis  in  order  that  each  milligram  of  Mg2P2O7  shall  repre- 
sent o.  i  per  cent  of  P  ?    0.2  per  cent  of  P2O5  ? 


STOICHIOMETRY  191 

56.  A  mixture  of  equal  parts  of  sodium  chloride  and  potassium 
chloride   weighs   0.30  gram.     How   many   cubic   centimeters   of 
platinic  chloride  solution  containing  o.i  gram  platinum  per  cubic 
centimeter  will  be  necessary  to  completely  change  the  sodium  and 
potassium  chlorides  to  the  chlorplatinates  ? 

2KCl+PtCl4=K2PtCl6. 

57.  10  grams  of  a  sample  of  soil  were  fused  with  sodium  car- 
bonate, dissolved  in  hydrochloric  acid  after  the  removal  of   the 
silica,  and  the  solution  made  up  to  500  c.c.     The  phosphorus  in 
200  c.c.  of  the  sample  was  precipitated  and  gave  on  ignition  0.072 
gram  of   Mg2P2O7.     100  c.c.  of  the  solution   were  titrated   with 
dichromate  solution  for  iron,  8.23  c.c.  of  the  dichromate  solution 
being  used,     (i  c.c.  K2Cr2O7  =  0.00072  gram  oxygen.)     The  iron, 
aluminium,  and  phosphorus  in  100  c.c.  of  the  solution  were  precipi- 
tated with  ammonium  hydroxide,  and  on  ignition  weighed  0.380 
gram.    Calculate  the  percentages  of  Fe2O3,  A12O3,  and  P  in  the  soil. 

58.  1.2  grams  of  a  silver  coin  were  dissolved  in  nitric  acid,  and 
the   silver   precipitated   with   normal  hydrochloric  acid,  9.10  c.c. 
being  used.     What  percentage  of  silver  was  in  the  coin  ? 

59.  To  a  solution  of  Glauber's   salt  N/io  BaCl2  solution  was 
added  until  no  more  precipitate  was  formed,  14.70  c.c.  of  the  solu- 
tion being  used.     Calculate  the  number  of  grams  of   anhydrous 
sodium  sulphate  in  the  solution. 

60.  13.48  c.c.  of  a  solution  of  standard  hydrochloric  acid  were 
necessary  to  dissolve  one  gram  of  pure  calcium  carbonate.     How 
many  cubic  centimeters  of  this  solution  must  be  taken  to  make  a 
liter  of  normal  acid  ? 

61.  How  many  cubic  centimeters  of  N/2  HC1  would  be  neces- 
sary to  dissolve  0.3  gram  of  witherite  (BaCO3)  which  contains  as 
an  impurity  7  per  cent  of  quartz  ? 

62.  How  many   cubic   centimeters  of   5.5   normal   ammonium 
hydroxide  solution  would  be  required  to  precipitate  the  aluminium 
in  one  gram  of  potassium  alum  ? 

63.  How  much  NaOH,  85  per  cent  pure,  must  be  added  to  2 
liters  of  a  NaOH  solution,  i  c.c.  of  which  is  equivalent  to  0.041 
gram  H2SO4,  in  order  to  make  the  solution  normal?     How  much 
water  should  be  added  to  make  it  N/3  ? 


192  QUANTITATIVE  ANALYSIS 

64.  1.2  grams  of  pure  ammonium  chloride  were  dissolved  in 
water   and  heated  with  an  excess  of   sodium  hydroxide  solution. 
The  ammonia  gas  was  conducted  into  water  and  neutralized  with 
standard    sulphuric    acid,   18.30   c.c.  being  used.     What  was  the 
normality  of  the  sulphuric  acid  ? 

65.  A   standard  solution  of  HC1  is  analyzed  by  precipitating 
with  AgNO3;    10  c.c.  of  the  acid  solution  gave  0.22  gram  AgCl. 
What  is  the  normality  of  the  acid  ?     What  weight  of  calcite  con- 
taining 0.3  per  cent  SiO2  as  an  impurity  will  be  dissolved  by  50 
c.c.  of  the  acid  ? 

66.  The  total  phosphorus  in  a  sample  of  0.22  gram  of  fertilizer 
was  precipitated  as  ammonium  phosphomolybdate.     The  precipi- 
tate was  dissolved  in  40  c.c.  of  N/3  potassium  hydroxide  solution 
and    the    excess    of    alkali    titrated    with    standard    nitric   acid 
(i  c.c.  =  1.021  c.c.  of  N/3  KOH),  14.20  c.c.  being  used.     Calculate 
the  percentage  of  phosphorus  in  the  sample. 

2(NH4)3PO4-  i2MoO3+46KOH 

=  2  (NH4)2HPO4  +  (NH4)2MoO4  +  23  K2MoO4  +  22  H2O. 

67.  A  sample  of  1.5  grams  of  feeding  material  was  weighed  out 
for  the  determination  of  total  proteids  by  the  Kjeldahl  method. 
The  ammonia  was  absorbed  in  25.00  c.c.  of  N/2  HC1.     The  excess 
of  acid  in  the  absorption  flask  was  neutralized  with  12.00  c.c.  of 
standard   ammonium    hydroxide    solution   (21.20   c.c.  =  18.00  c.c. 
N/2  HC1).     Calculate  the  percentage  of  total  proteids  in  the  sample. 
Use  6.25  as  the  factor  for  the  conversion  of  nitrogen  to  proteids. 

68.  In  the  determination  of   the  Reichert-Meissl   number   for 
butter  fat  as  described  on  page  no,  a  sample  of  5.023  grams  was 
taken  for  analysis.     The   total  distillate   containing   the   volatile 
acids  was  no  c.c.;    100  c.c.  of  this  solution  required  12.50  c.c.  of 
KOH  (i  c.c.  =  1.092  c.c.  N/io  KOH)  for  neutralization.     Calculate 
the  Reichert-Meissl  number. 

69.  In  the  determination  of  the  saponification  number  of  butter 
fat,  as  described  on  page  115,  1.740  grams  of  the  sample  were  taken 
for  analysis.     On  titrating  the  blank,  69.70  c.c.  of  HC1  were  used, 
while  the  sample  required  46.75  c.c.  HC1.     i  c.c.  HC1  =  0.01014 
gram  of  HC1.     Calculate  the  saponification  number. 

70.  A  sample  of  9.200  grams  of  butter  fat  was  used  for  the  de- 
termination of  salt,  which  was  extracted  with  water  (see  page  102) 


STOICHIOMETRY  193 

and  the  solution  made  up  to  200  c.c.  50  c.c.  of  the  salt  solution  re- 
quired 14.40  c.c.  of  N/20  AgNOg  solution  for  titration.  Calculate 
the  percentage  of  salt  in  the  butter. 

71.  A  sample  of  0.5  gram  of  siderite  (FeCO3),  the  only  impurity 
in  which  is  3.5  per  cent  quartz,  is  dissolved  out  of  contact  with 
the  air.     How  many  cubic  centimeters  of  permanganate  solution 
(i  c.c.  =  0.008  gram  of  H2C2O4  •  2  H2O)  will  be  required  to  oxidize 
the  iron  ? 

72.  0.5  gram  of  a  sample  of  ferrous  ammonium  sulphate  which 
had  been  heated,  was  dissolved  and  titrated  with  N/io  KMnO4, 
16.80  c.c.  being    required.     What   percentage   of    the   water   of 
crystallization  had  been  lost  ? 

73.  A  sample  of  0.5  gram  of  an  iron  ore  was  titrated  for  iron 
with  N/io  KMnO4  solution,  27.80  c.c.  being  used.     If  the  student 
neglected  to  apply  the  calibration  correction  of   +0.14  c.c.,  what 
would  be  the  error  in  the  percentage  of  iron  as  reported  ? 

74.  One    cubic  centimeter  of  a   solution   of    KMnO4   contains 
0.00042  gram  of  available  oxygen.     How  much    oxygen  will  be 
available  when  the  permanganate  is  used  for  titration  in  a  neutral 
solution  ? 

2  KMnO4  =  K2O  +  MnO2  +30. 

75.  What  weight  of  iron  wire  99.7  per  cent  pure  will  be  oxi- 
dized by  the  potassium   dichromate  formed  from    0.35  gram  of 
chrome  iron  (FeO  •  Cr2O3)  the  only  impurity  in  which  is  4.5  per 
cent  silica  ? 

76.  25.00  c.c.  of  a  solution  of  potassium  permanganate,  on  being 
added  to  a  solution  of  potassium  iodide  in  sulphuric  acid,  liberated 
0.33  gram  of  iodine.     To  what  volume  should  one  liter  of  the  solu- 
tion be  diluted  to  make  it  exactly  tenth  normal  ? 

77.  Some   crystallized    sodium    thiosulphate  (Na2S2O3  •  5  H2O) 
was   exposed   to   the   air   and   lost   water   of   crystallization.      A 
sample  of  0.62  gram  was  dissolved  in  water  and  titrated  with  an 
iodine  solution  (i  c.c.  =  0.0049  gram  As2O3),  28.10  c.c.  being  used 
in  the  titration.     What  percentage  of  the  water  of  crystallization 
had  been  lost?     How  many   grams    of  the  sodium   thiosulphate 
should  be  weighed  out  for  a  liter  of  N/io  solution? 

78.  A  sample  of  0.5347  gram  of  pyrolusite  was  weighed  out  for 
analysis,  into  a  retort.     It  was  heated  with  hydrochloric  acid  and 


194  QUANTITATIVE  ANALYSIS 

the  chlorine  evolved  passed  into  a  solution  of  potassium  iodide. 
The  iodine  solution  was  diluted  to  250  c.c.,  and  100  c.c.  titrated 
with  N/io  Na2S2O3  solution  of  which  21.90  c.c.  were  used.  Cal- 
culate (a)  the  purity  of  the  pyrolusite ;  (b)  the  oxidizing  power  of 
one  gram  in  terms  of  iron  and  crystallized  oxalic  acid. 

79.  In  the  determination  of  the  iodine  absorption  number  by  the 
Hanus  method  described  on  page  117,  0.7380  gram  of  butter  fat 
was  taken  for  analysis.     On  titrating 

Blank  required  32.40  c.c.  Na2S2O3  solution, 
Sample  required  11.30  c.c.  Na2S2O3  solution. 

2O   c.c.    K2Cr2O7  solution   are  equivalent   to    16.20  c.c.  Na2S2O3. 

i  c.c.  of  the  K2Cr2O7  contains  0.00387  gram  of  the  dichromate. 

Calculate  the  iodine  absorption  number. 

80.  Cupric  salts  in  a  solution  of  potassium  iodide  containing 
acetic  acid   are  reduced   to  cuprous  salts  with  the   liberation  of 
iodine.     The  iodine  can  then  be  titrated  in  the  usual  way  with 
sodium  thiosulphate  solution. 

2  Cu(C2H302)2  4-  4  KI  =  Cu2I2  +  4  KC2H3O2  +  I2. 

How  many  grams  of  copper  will  furnish  the  iodine  necessary  to 
react  with  18.00  c.c.  of  N/io  Na2S2O3  solution  ? 


APPENDIX 

BOOKS  OF  REFERENCE 

Agricultural  Analysis 

ALLEN,  A.  H.     Commercial  Organic  Analysis.    4  Vols. 

BLYTHE,  A.  W.     Foods,  Their  Composition  and  Analysis.     5th  Edition  (1903). 

INGLE,  H.     Manual  of  Agricultural  Chemistry  (1902). 

JAGO,  W.     The  Science  and  Art  of  Bread  Making. 

Chemistry  and  Analysis  of  Wheat,  Flour,  etc.  (1895). 

KONIG,  J.     Untersuchung  Landwirtschaftlich  und  Gewerblich  Wichtiger  Stoffe 

(1906). 

LEACH,  A.  E.     Food  Inspection  and  Analysis  (1904). 
LEFFMAN  AND  BEAM.     Select  Methods  of  Food  Analysis  (1905). 
RICHMOND,  H.  D.     Dairy  Chemistry. 
SHERMAN,  H.  C.     Organic  Analysis  (1905). 
SNYDER,  H.     Dairy  Chemistry  (1906).     Contains  an  excellent  Bibliography,  page 

161. 

Soils  and  Fertilizers  (1905). 

United  States  Department  of  Agriculture,  Division  of  Chemistry,  Bulletin  No. 

46   (1898),  Methods  of  Analysis  adopted   by  the  Association  of  Official 

Agricultural  Chemists. 
United  States  Department  of  Agriculture,  Bureau  of  Chemistry,  Bulletin  No.  65 

(1902),  Provisional  Methods  for   the  Analysis  of  Foods   adopted  by  the 

Association  of  Official  Agricultural  Chemists. 
WILEY,  H.  W.     Foods  and  their  Adulteration  (1907). 

Principles  and  Practice  of  Agricultural  Analysis. 

Vol.  i.  —  Soils  (1906). 

Vol.  2.  —  Fertilizers  (New  Edition  in  Press). 

Vol.  3.  —  Agricultural  Products  (1897). 

General  Quantitative  Chemical  Analysis 

CLASSEN,  A.     Ausgewahlte  Methoden  der  Analytischen  Chemie.     2  Vols.  (1901). 

COHN.     Indicators  and  Test  Papers  (1899). 

FRESENIUS.     Quantitative   Chemical  Analysis.     2  Vols.     Translated   by  Cohn 

(1904). 
HILLEBRAND,  W.  F.     The  Analysis  of  Silicate  and  Carbonate  Rocks.     United 

States  Geological  Survey,  Bulletin  No.  305. 
JULIAN,  F.     Quantitative  Chemical  Analysis  (1902). 
OLSEN,  J.  C.     Quantitative  Chemical  Analysis  (1904). 
SUTTON,  F.     Volumetric  Analysis,  9th  edition. 

TREADWELL-HALL.     Analytical  Chemistry,  Vol.  II,  Quantitative  Analysis. 

195 


196 


QUANTITATIVE  ANALYSIS 


The  Application  of  the  Modern  Theories  of  Chemistry  to  Quantitative  Analysis 

ABEGG,  A.     The  Electrolytic  Dissociation  Theory.     Translated  by  von  Ende. 
BOTTGER,  W.     The  Principles  of  Qualitative  Analysis  from  the  Standpoint  of 

the   Theory   of  Electrolytic   Dissociation  and  the   Law  of  Mass   Action. 

Translated  by  Smeaton. 
OSTWALD,  W.     The  Scientific  Foundations  of  Analytical  Chemistry.     Translated 

by  McGowan. 
TALBOT  AND  BLANCHARD.     The  Electrolytic  Dissociation  Theory. 


TABLE   I 
DESK  REAGENTS 

The  reagents  placed  on  the  students1  desks  have  the  following  concentrations. 
When  concentrated  and  dilute  acids  are  referred  to  in  the  procedure,  these  acids 
should  be  used. 


HC1 

concentrated 

sp.  gr. 

1.  12 

contains  23.82  per  cent  HC1. 

HC1 

dilute 

sp.  gr. 

I.O4 

contains    8.16  per  cent  HC1. 

HNO3 

concentrated 

sp.  gr. 

1.42 

contains  69.80  per  cent  HNO3. 

HNO8 

dilute 

sp.  gr. 

1.20 

contains  32  36  per  cent  HNO3. 

H2SO4 

dilute 

sp.  gr. 

I.  II 

contains  15.71  per  cent  H2SO4. 

NH4OH 

sp.  gr. 

0.96 

contains    9.91  per  cent  NH3. 

TABLE  II 
LABORATORY  REAGENTS 


Name 

Descrip- 
tion 

Formula 

Molecu- 
lar 
Weight 

Grams 
per 
Liter 

Specific 
Gravity  at 
15°  C. 

Remarks,  Preparation, 
etc. 

Acid,  acetic 



HC2H302 

60.03 





99.5  per  cent.  (Glacial) 

Acid,  acetic 

Solution 







1.0412 

30  per  cent. 

Acid,     hydro- 

Solution 

HC1 

36-46 

469.00 

1.20 

39.11  per  cent. 

chloric 

Acid,    hydro- 





267.00 

1.  12 

23.82  per  cent.    3  vols. 

chloric 

of  acid  sp.  gr.  1.20 

to  2  vols.  water. 

Acid,    hydro- 

Solution 





255-00 

I.IX5 

22.86  per  cent. 

chloric 

. 

Acid,    hydro- 

Solution 





85.00 

1.04 

8.16  per  cent. 

chloric 

Acid,    hydro- 

Solution 





18.23 



N/2 

chloric 

Acid,     hydro- 

Solution 





9.12 



N/4 

chloric 

APPENDIX 


197 


TABLE   II  — Continued 


Name 

Descrip- 
tion 

Formula 

Molecu- 
lar 
Weight 

Grams 
per 
Liter 

Specific 
Gravity  at 
15°  C. 

Remarks,  Preparation, 
etc. 

Acid,  nitric 



HN08 

63.02 

991.00 

1.42 

69.8  per  cent 

Acid,  nitric 

Solution 





388.00 

1.20 

32.36  per  cent.    Made 

by  diluting  2  vols. 

of  sp.  gr.  1.42  with 

3  vols.  of  water 

Acid,  oxalic 



[H2C204  • 

126.05 







2H20] 

Acid,  salicylic 



[C6H4(OH) 

138-05 







COOH] 

Acid,  sulphuric 



H2S04 

98.08 

1759.00 

1.84 

95.6  per  cent  H2SO4 

Acid,  sulphuric 









1.82 

Commercial  —  for 

Babcock  test 

Acid,  sulphuric 

Solution 





702.00 

1.40 

50.11  per  cent  H2SO4 

Acid,  sulphuric 

Solution 





175.00 

I.  II 

15.71  per  cent  H2SO4 

Acid,  sulphuric 

Solution 





12-5 



1.25    per     cent  —  for 

crude  fiber 

Acid,  tartaric 



H2C4H406 

150.05 





Alcohol 



C2H6OH 

46.05 



0.8164 

95  per  cent  by  volume 

Alcohol 

Solution 







0.8639 

80  per  cent  by  volume 

Ammonium  car- 



[(NH4)2C03- 

114.1 





bonate 

H2O] 

Ammonium 



NH4C1 

53-49 





chloride 

Ammonium 

Solution 





200.00 



Saturated  with 

chloride 

K2PtCl6.    See  page 

201 

Ammonium 

Solution 

[(NH4)3C6 

243-  J7 



1.00-20° 

For     preparation     of 

citrate 

H507] 

solution     see    page 

201 

Ammonium 

Solution 

NH4OH 

35-05 



0.96 

9.91  per  cent  NH3 

hydroxide 

Ammonium 

Solution 

[(NH4)2Mo 

196.08 

6ogrs. 



For     preparation     of 

molybdate 

04] 

Mo03 

solution     see    page 

201 

Ammonium 



NH4NO3 

80.05 





nitrate 

Ammonium 

Solution 





100.0 



nitrate 

Ammonium 

Solution 

[(NH4)2C2 

142.1 

42.00 



Saturated  solution  at 

oxalate 

04-H20] 

15° 

Arseaious  oxide 



As.203 

198.00 





Asbestos 











For  Gooch  crucibles. 

For  preparation  see 

page  201 

Barium  chloride 

Solution 

[BaCl2  • 

244-33 

I22.OO 



2H20] 

Barium  hydrox- 

Solution 

[Ba(OH)2. 

3I5-5 

50 



Saturated  solution 

ide 

8H20] 

at  20° 

198 


QUANTITATIVE  ANALYSIS 


TABLE   II  — Continued 


Name 

Descrip- 
tion 

Formula 

Molecu- 
lar 
Weight 

Grams 
per 
Liter 

Specific 
Gravity  at 
15°  C- 

Remarks,  Preparation, 
etc. 

Bromine  water 

Solution 

Br2 

IS9-92 





Water   at  room  tem- 

perature    saturated 

with  liquid  bromine 

with  a  few  drops  of 

bromine  in  the  bot- 

tom of  the  bottle. 

Calcium  carbon- 



CaCO3 

IOO.I 





For  standardising  so- 

ate 

lutions.          Iceland 

spar,    or    the    pure 

precipitated       sub- 

stance 

Calcium    chlo- 



CaCl2 

III.OO 





Granular.       For    ab- 

ride 

sorbing  moisture 

Chloroform 



CHC13 

119.36 





Copper  sulphate 



[CuS04  • 

249.74 





5H20] 

Ether,  ethyl 



(C2H6)20 

74.08 





For    extracting    fats. 

Dry.    Distilled  from 

sodium 

Fehling's  copper 

Solution 









69.27  grams  CuSO4  • 

solution 

5  H2O  per  liter 

Fehling's    alkali 

Solution 









356    grams    Rochelle 

solution,      for 

salts  and  100  grams 

lactose,         by 

NaOH  in  one  liter 

S  o  x  h  1  e  t's 

method 

Fehling's    alkali 

Solution 









356    grams     Rochelle 

solution       for 

salts  and  250  grams 

use  in  Allihn's 

KOH  in  one  liter 

method       for 

dextrose 

Ferrous    ammo- 



[FeSO4 

392.20 





. 

nium  sulphate 

(NH4)2S04- 

6H20] 

Iodine 



Is 

253-94 





Iodine       mono- 

Solution 

IBr 

206.93 





For  preparation  of  so- 

bromide 

lution  see  page  116 

Iron 



Fe 

55-9 





Pure,  electrolytic 

Litmus  paper 











Magnesite 



MgCOg 

84-36 





Magnesium  mix- 

Solution 

[MgCla+ 







Dissolve    no     grams 

ture 

NH4C1+ 

of  crystallized  mag- 

NH4OH] 

nesium         chloride 

(MgCl2.6H2O)and 

40   grams    of    am- 

monium chloride  in 

1300  c.c.  of  water  and 

make  up  to  two  liters 

with  ammonium  hy- 

droxide (sp.  gr.  0.96) 

APPENDIX 


199 


TABLE   II  —  Continued 


Name 

Descrip- 
tion 

Formula 

Molecu- 
lar 
Weight 

Grams 
per 
Liter 

Specific 
Gravity  at 
15°  C. 

Remarks,  Preparation, 
etc. 

Magnesium    ox- 



MgO 

40.36 





ide 

Malt  extract 

Solution 









For  preparation,  see 

page  127 

Mercury 



Hg 

200.00 





Mercuric     chlo- 

Solution 

HgCl2 

270.9 

50.0 



ride 

Methyl     orange 

Solution 





I.  CO 



Dissolve   i    gram    in 

(orange     No. 

one  liter  of  water 

Ill) 

Molybdic  oxide 



MoO3 

144.00 





Paraffine 











Phenolphthalein 

Solution 





5.00 



Dissolve  5  grams  in 

one  liter  of  60  per 

cent  alcohol.    Filter 

Platinic  chloride 

Solution 

PtCl4 

336.6 

172.8 



I  c.c.  of  solution  con- 

tains   o.i   gram    of 

platinum 

Potassium  chro- 

Solution 

K2CrO4 

194.4 

100.00 



Indicator  for  determi- 

mate 

nation  of  chlorine 

Potassium       di- 



K2Cr207 

294-5 





chromate 

Potassium  ferri- 



K8Fe(CN)6 

329.42 





cyanide 

Potassium      hy- 



KOH 

56.16 





droxide 

Potassium      hy- 

Solution 

KOH 



40.00 



Dissolve  in  one  liter 

droxide 

of  redistilled  95  per 

cent  alcohol 

Potassium       io- 



KI 

166.12 





dide 

Potassium       io- 

Solution 

KI 



150.00 



dide 

Potassium     per- 



KMnO4 

158.15 





manganate 

Potassium     sul- 

Solution 

K2S 

110.36 

40.00 



phide 

Pumice 







— 



Ignited    at    red    heat 

and    plunged    into 

cold   water.      Kept 

under  water 

Rochelle  salt 



[KNaC4H4 

282.3 





06.4H20] 

Silver  nitrate 

Solution 

AgN03 

169.94 

ICO.OO 



Silver  nitrate 

Solution 





8.499 



N/20  —  for  determina- 

tion of  salt  in  butter 

Sodium        acid 



NaHCO8 

84.06 





carbonate 

20O 


QUANTITATIVE  ANALYSIS 


TABLE   II  — Continued 


Name 

Descrip- 
tion 

Formula 

Molecu- 
lar 
Weight 

Grams 
per 
Liter 

Specific 
gravity  at 
15°  C. 

Remarks,  Preparation, 
etc. 

Sodium  "ammo- 

Solution 

[NaNH4 

209.16 

100.00 



nium  hydro- 

HP04 • 

gen  phosphate 

4H20] 

(microcosmic 

'" 

salt) 

Sodium  carbon- 



Na2CO3 

106.10 





ate 

Sodium   dichro- 



[NasCrsOr 

298.33 





Commercial.          For 

mate 

2H20] 

cleaning     solution. 

See  page  45 

Sodium  hydrox- 



NaOH 

40.06 





ide 

Sodium  hydrox- 

Solution 









One  part  sodium  hy- 

ide 

droxide  to  one  part 

of  water 

Sodium  hydrox- 

Solution 





600.00 



600  grams  of  commer- 

ide 

cial      (Greenbank) 

alkali   dissolved  in 

one  liter  of  water 

Sodium  hydrox- 

Solution 





20.03 



N/2 

ide 

Sodium  hydrox- 

Solution 





4.006 



N/io 

ide 

Sodium  hydrox- 

Solution 





12.5 



1.25  per  cent.      For 

ide 

crude    fiber    deter- 

minations 

Sodium  oxalate 



Na2C204 

134.10 





For    preparation,  see 

page  72 

Sodium  thiosul- 



[Na^CV 

248.30 





phate 

5H20] 

Stannous  chlor- 

Solution 

SnCl2 

189.9 





Dissolve  30  grams  of 

ide 

tin    in    125    c.c.  of 

HC1  (sp.  gr.  1.  20). 

Dilute   to   250    c.c. 

and  filter.    Add  250 

cc.    HC1    (sp.    gr. 

1.12)  and  make  up 

to  i  liter  with  water. 

Add  a  few  pieces  of 

granulated  tin 

Starch 



(C6H1006)« 







For     indicator,      see 

page  80 

Sugar  (sucrose) 



C12H22On 

342.18 





Water—  nitro- 



H2O 

18.016 





See  page  201 

gen-free 

Wool,  glass 











Zinc 



Zn 

654 





Dust 

Zinc 











Granulated 

Zinc 











For  Jones  Reductor 

APPENDIX  201 


Ammonium  Citrate  Solution 

Dissolve  370  grams  of  commercial  citric  acid  in  1 500  c.c.  of  water ;  nearly  neu- 
tralize with  ammonium  hydroxide ;  cool,  add  ammonium  hydroxide  until  exactly 
neutral  (tested  with  a  saturated  alcoholic  solution  of  corallin)  and  dilute  the  vol- 
ume to  2  liters.  Determine  the  specific  gravity,  which  should  be  1.09  at  20°. 
For  another  method  of  preparing  this  solution,  see  U.S.  Department  of  Agricul- 
ture, Bull.  No.  46,  page  n. 

Asbestos  for  Gooch  Crucibles 

Select  a  grade  of  asbestos  having  long  fibers,  soak  it  with  water,  shred  it  in  a 
porcelain  mortar.  Treat  it  with  hydrochloric  acid  (sp.  gr.  1.12)  for  twelve 
hours,  wash  it  by  decanting  with  distilled  water  several  times,  allowing  the  fine 
particles  of  fiber  to  be  decanted  with  the  distilled  water.  Filter,  wash  well,  dry, 
and  ignite  in  a  platinum  dish  with  the  blast  lamp.  I. 

Ammonium  Chloride  Solution  saturated  with  Potassium  Chlorplatinate 

Dissolve  100  grams  of  ammonium  chloride  in  500  c.c.  of  water,  add  from  5 
to  10  grams  of  pulverized  potassium  chlorplatinate,  allow  to  stand  for  six  or  eight 
hours,  shaking  at  intervals.  Allow  the  mixture  to  settle  overnight,  then  filter. 
The  residue  may  be  used  for  the  preparation  of  a  fresh  supply. 

Ammonium  Molybdate  Solution 

Dissolve  100  grams  of  molybdic  acid  (MoO3)  in  417  c.c.  of  ammonium  hydrox- 
ide (sp.  gr.  0.96)  and  slowly  pour  the  solution  thus  obtained  into  1250  c.c.  of 
nitric  acid  of  specific  gravity  i  .20.  Keep  the  mixture  in  a  warm  place  for  several 
days  or  until  a  portion  heated  to  40°  deposits  no  yellow  precipitate  of  ammonium 
phosphomolybdate. 

Preparation  of  Nitrogen-free  Water 

Add  to  a  carboy  of  ordinary  distilled  water  enough  bromine  water  to  give  it  a 
distinct  color.  Allow  to  stand  for  a  day  or  two,  then  add  an  excess  of  sodium 
carbonate  and  distill  in  a  room  free  from  ammonia  fumes.  The  distillate  will  be 
ammonia-free. 


2O2 


QUANTITATIVE  ANALYSIS 


TABLE   III 
APPARATUS  FOR  DESK  EQUIPMENT 


Beakers,  nests  0-6 2 

Bottles,  glass-stoppered,  i\  liter  .  2 

Brush,  camePs-hair I 

Burette,  glass  stopcock,  30  c.c.  .  I 

Burette,  pinchcock,  30  c.c.  .  .  I 

Burette  holder i 

Burners,  adjustable 2 

Casseroles,  250  c.c 2 

Cover-glasses,  50  mm 2 

Cover-glasses,  75  mm 2 

Cover-glasses,  125  mm 2 

Crucibles,  porcelain,  No.  oo  .  .  4 

Cylinder,  graduated,  50  c.c.  .  .  I 

Desiccator,  for  four  crucibles  .  .  I 
Dishes,  porcelain  evaporating,  5  cm. 

diam 2 

File i 

Filter  papers,  ashless  —  gem.  .  50 

Filter  papers,  ashless  —  n  cm.  .  10 

Filter  papers,  qualitative,  9  cm.  .  25 

Filter  papers,  hardened,  half  form  4 

Flasks,  Erlenmeyer,  250  c.c.  .  .  4 

Flasks,  Jena  Erlenmeyer,  125  c.c.  2 

Flasks,  Kjeldahl,  500  c.c.  ...  2 

Flasks,  plain,  250  c.c.  .....  2 

Flasks,  plain,  500  c.c 2 

Flasks,  volumetric,  glass-stoppered, 

250  c.c 2 

Flasks,  volumetric,  glass-stoppered, 

500  c.c i 

Flasks,  volumetric,  glass-stoppered, 

1000  c.c i 

Forceps,  steel,  130  mm.  ...  i 

Funnels,  75  mm.,  stem  200  mm.  .  4 

Funnels,  25  mm.,  stem  50  mm.  .  2 

Indicators,  50  c.c.  flasks  of  ...  2 


Lock  and  key    . 
Matches  —  boxes  . 
Notebook     .... 
Pan,  15  cm.  diameter 
Paper,  sheets  of  glazed 
Pinchcock    .... 
Pipettes, 


5  c.c 

10  c.c 

10  c.c.  graduated  . 

25  c.c 

50  c.c 

100  c.c 

Policemen,  rubber 


Reagent  bottles,  30  c.c.,  for  silver 

nitrate I 

Rod,  glass,  feet  of 2 

Sponge  i 

Stand,  filter i 

Stands,  iron,  with  two  rings 

each 2 

Stopper,  rubber,  No.  5  ....  i 

Tongs,  brass  ....  .  .  i 

Towel i 

Triangles,  pipe  stem,  new  form  .  2 

Tripods 2 

Tubes,  inner  extraction,  length  85 

mm.,  diam.  25  mm 2 

Tubes,  inner  extraction,  length  70 

mm.,  diam.  18  mm 2 

Tubes,  weighing,  with  corks  .  .  3 

Tubing,  glass,  i"  diam.,  feet  3 

Tubing,  rubber,  J"  diam.,  feet  6 

Tubing,  "  Ty  diam.,  foot  i 

Wire  gauze,  asbestos  center  .  .  2 

Wire,  platinum,  inches  ....  3 


APPENDIX 


203 


TABLE   IV 

SPECIFIC  GRAVITY  OF  HYDROCHLORIC,  NITRIC,  AND  SULPHURIC  ACIDS 

G.  Lunge 


Specific 
Gravity 

3 

(Vacuo) 

Per  Cent  by  Weight 

Specific 
Gravity 

«f 

(Vacuo) 

Per  Cent  by  Weight 

HCl 

HNO, 

H2S04 

HN03 

H2S04 

.OOO 

0.16 

O.IO 

0.09 

1.205 

33.09 

27.95 

.005 

I.I5 

1.  00 

0.83 

1.  210 

33.82 

28.58 

.OIO 

2.14 

1.90 

1-57 

I.2I5 

34.55 

29.21 

.015 

3.12 

2.80 

2.30 

I.22O 

35.28 

29.84 

.020 

4-13 

3.70 

3-03 

1.225 

36.03 

30.48 

.025 

5-15 

4.60 

3.76 

1.230 

36.78 

3I.II 

.030 

6.15 

5.50 

4.49 

1.235 

37-53 

31.70 

•035 

7.15 

6.38 

5.23 

1.240 

38.29 

32.28 

.040 

8.16 

7.26 

5.96 

1.245 

39.05 

32.86 

.045 

9.16 

8.13 

6.67 

1.250 

39.82 

33-43 

.050 

10.17 

8.99 

7-37 

1.255 

40.58 

34.00 

.055 

II.I8 

9.84 

8.07 

1.260 

41-34 

34-57 

.060 

12.19 

10.68 

8.77 

1.265 

42.10 

35.H 

.065 

I3-I9 

11.51 

9-47 

1.270 

42.87 

35-71 

.070 

14.17 

12.33 

10.19 

1.275 

43-64 

36-29 

.075 

15.16 

13-15 

10.90 

1.280 

44.41 

36.87 

.080 

I6.I5 

13-95 

ii.  60 

1.285 

45.18 

37-45 

.085 

17.13 

14.74 

12.30 

1.290 

45-95 

38.03 

.090 

18.11 

15-53 

12.99 

1.295 

46.72 

38.61 

.095 

19.06 

16.32 

13.67 

1.300 

47-49 

39-19 

.100 

20.01 

17.11 

14-35 

1.305 

48.26 

39-77 

.105 

20-97 

17.89 

15-03 

I.3IO 

49.07 

40.35 

.110 

21.92 

18.67 

15.71 

L3I5 

49.89 

40.93 

.115 

22.86 

J9-45 

16.36 

1.320 

50.71 

41.50 

.120 

23.82 

20.23 

17.01 

L325 

5L53 

42.08 

.125 

24.78 

21.00 

17.66 

1-330 

52-37 

42.66 

.130 

25-75 

21.77 

18.31 

1-335 

53-22 

43.20 

•135 

26.70 

22.54 

1  8..  96 

1.340 

54.07 

43-74 

.140 

27.66 

23.31 

19.61 

1-345 

54-93 

44.28 

.145 

28.61 

24.08 

20.26 

1-350 

55-79 

44.82 

.150 

29.57 

24.84 

20.91 

1-355 

56.66 

45-35 

•155 

30-55 

25.60 

21.55 

1.360 

57-57 

45.88 

.I60 

31.52 

26.36 

22.19 

1-365 

58.48 

46.41 

.165 

32.49 

27.12 

22.83 

1.370 

59-39 

46.94 

.170 

33-46 

27.88 

2347 

1-375 

60.30 

47-47 

•175 

34.42 

28.63 

24.12 

1.380 

61.27 

48.00 

.180 

35.39 

29.38 

24.76 

1-385 

62.24 

48.53 

.185 

36.31 

30.I3 

25.40 

1.390 

63-23 

49.06 

.190 

37.23 

30.88 

26.04 

1-395 

64.25 

49-59 

.195 

38.16 

31.62 

26.68 

1.400 

65.30 

50.11 

.200 

39.  II 

32.36 

27.32 

1.405 

66.40 

50.63 

2O4 


QUANTITATIVE  ANALYSIS 


TABLE  IV—  Continued 


Specific 
Gravity 
at  15! 
4° 
(Vacuo) 

Per  Cent  by  Weight 

Specific 
Gravity 

15° 

att 
(Vacuo) 

Per  Cent 
by 
Weight 

Specific 
Gravity 

-* 

(Vacuo) 

Per  Cent 
by 
Weight 

HNO3 

H2S04 

H2SO4 

H2S04 

1.405 

66.40 

50.63 

1.570 

65.90 

•730 

79.80 

I.4IO 

67.50 

51.15 

1-575 

66.30 

•735 

80.24 

I.4I5 

68.63 

51.66 

1.580 

66.71 

.740 

80.68 

I.42O 

69.80 

52.15 

1.585 

67.13 

•745 

8I.I2 

1.425 

70.98 

52.63 

1.590 

67.59 

.750 

81.56 

1.430 

72.17 

53-11 

J-595 

68.05 

•755 

82.00 

1-435 

73.39 

53-59 

i.  600 

68.51 

.760 

82.44 

1.440 

74.68 

54.07 

1.605 

68.97 

.765 

82.88 

1.445 

75.98 

54.55 

1.610 

6943 

•770 

83-32 

1.450 

77.28 

55'°3 

1.615 

69.89 

•775 

83.90 

M55 

78.60 

55.50 

1.620 

70.32 

.780 

84.50 

1.460 

79.98 

55-97 

1.625 

70.74 

.785 

85.10 

1.465 

81.42 

56.43 

1.630 

7I.l6 

.790 

85.70 

1.470 

82.90 

56.90 

1-635 

7L57 

•795 

86.30 

1-475 

84.45 

57-37 

1.640 

71.99 

.800 

86.90 

1.480 

86.05 

57-83 

1.645 

72.40 

.805 

87.60 

1.485 

87.70 

58.28 

1.650 

72.82 

.810 

88.30 

1.490 

89.60 

58.74 

1.655 

73-23 

.815 

89.05 

1.495 

91.60 

59.22 

i.  660 

73-64 

.820 

90.05 

1.500 

94.09 

59.70 

1.665 

74.07 

.825 

91.00 

1.505 

96.39 

60.18 

1.670 

74.51 

.830 

92.10 

1.510 

98.10 

60.65 

1.675 

7497 

-835 

93-43 

1-515 

99.07 

61.12 

i.  680 

75  42 

.840 

95.60 

1.520 

99.67 

61.59 

1.685 

75.86 

.8405 

95-95 

1.525 

62.06 

1.690 

76.30 

.8410 

97.00 

1-530 

62.53 

1.695 

76.73 

.8415 

97-70 

1-535 

63.00 

1.700 

77.17 

.8410 

98.20 

1.540 

63-43 

1.705 

77.60 

.8405 

98.70 

1-545 

63.85 

1.710 

78.04 

.8400 

99.20 

1.550 

64.26 

1.715 

78.48 

•8395 

99-45 

1-555 

64.67 

1.720 

78.92 

.8390 

99-70 

1.560 

65.08 

1.725 

79.36 

.8385 

99-95 

1.565 

65.49 

APPENDIX 


205 


TABLE   V 

SPECIFIC  GRAVITY  OF  AMMONIA  SOLUTIONS  AT  15°  C. 
Lunge  and  Wiernik 


Specific  Gravity 

Per  Cent  NH3 

Specific  Gravity 

Per  Cent  NH3 

1.  000 

0.00 

0.940 

I5-63 

0.998 

0.45 

0.938 

16.22 

0.996 

0.91 

0.936 

16.82 

0.994 

i-37 

0-934 

17.42 

0.992 

1.84 

0.932 

18.03 

0.990 

2.31 

0.930 

18.64 

0.988 

2.80 

0.928 

19.25 

0.986 

3-30 

0.926 

19.87 

0.984 

3.80 

0.924 

20.49 

0.982 

4-30 

0.922 

21.12 

0.980 

4.80 

0.920 

21.75 

0.978 

5-30 

0.918 

22.39 

0.976 

5.80 

0.916 

23.03 

0.974 

6.30 

0.914 

23.68 

0.972 

6.80 

0.912 

24.33 

0.970 

7-3i 

0.910 

24-99 

0.968 

7.82 

0.908 

25.65 

0.966 

8.33 

0.906 

26.31 

0.964 

8.84 

0.904 

26.98 

0.962 

9-35 

0.902 

27.65 

0.960 

9.91 

0.900 

28.33 

0.958 

10.47 

0.898 

29.01 

0.956 

11.03 

0.896 

29.69 

0.954 

1  1.  60 

0.894 

30.37 

0.952 

12.17 

0.892 

3L05 

0.950 

12.74 

0.890 

31-75 

0.948 

I3-3I 

0.888 

32.50 

0.946 

13.88 

0.886 

33-25 

0.944 

14.46 

0.884 

34.10 

0.942 

15.04 

0.882 

34-95 

206 


QUANTITATIVE  ANALYSIS 


TABLE  VI 
DETERMINATION  OF  LACTOSE  BY  SOXHLET'S  METHOD1 


Milli- 
grams of 
copper 

Milli- 
grams of 
lactose 

Milli- 
grams of 
copper 

Milli- 
grams of 
lactose 

Milli- 
grams  of 
copper 

Milli- 
grams of 
lactose 

Milli- 
grams of 
copper 

Milli- 
grams ol 
lactose 

Milli- 
grams of 
copper 

Milli- 
grams of 
lactose 

100 

71.6 

138 

99-8 

I76 

128.5 

214 

157-5 

252 

186.3 

101 

72.4 

139 

100.5 

177 

129.3 

2I5 

158.2 

253 

187.1 

102 

73-i 

140 

101.3 

I78 

I3O.I 

216 

159.0 

254 

187.9 

103 

73-8 

141 

102.0 

I79 

130.8 

217 

J59-7 

255 

188.7 

104 

74.6 

142 

102.8 

1  80 

I3I.6 

218 

160.4 

256 

189.4 

105 

75-3 

143 

103-5 

181 

132.4 

2I9 

161.2 

257 

190.2 

1  06 

76.1 

144 

104.3 

182 

I33-I 

220 

161.9 

258 

I9I.O 

107 

76.8 

145 

105.1 

183 

133-9 

221 

162.7 

259 

I9I.8 

108 

77.6 

146 

105.8 

184 

134-7 

222 

163.4 

260 

192.5 

109 

78.3 

147 

106.6 

185 

135-4 

223 

164.2 

26l 

J93-3 

IIO 

79.0 

148 

107.3 

186 

136.2 

224 

164.9 

262 

194.1 

in 

79-8 

149 

108.1 

187 

137.0 

225 

165.7 

263 

194.9 

112 

80.5 

150 

108.8 

1  88 

137-7 

226 

166.4 

264 

195-7 

H3 

81.3 

151 

109.6 

189 

138.5 

227 

167.2 

265 

196.4 

114 

82.0 

I52 

110.3 

190 

J39-3 

228 

167.9 

266 

197.2 

II5 

82.7 

153 

in.  i 

191 

140.0 

229 

1  68.  6 

267 

198.0 

116 

83-5 

154 

111.9 

192 

140.8 

230 

169.4 

268 

198.8 

117 

84.2 

155 

112.  6 

193 

141.6 

231 

170.1 

269 

199.5 

118 

85.0 

I56 

ii3-4 

194 

142.3 

232 

170.9 

270 

200.3 

119 

85.7 

157 

114.1 

195 

I43-I 

233 

171.6 

271 

20  1.  1 

120 

86.4 

I58 

114.9 

196 

H3-9 

234 

172.4 

272 

201.9 

121 

87.2 

J59 

115.6 

197 

144.6 

235 

I73-I 

273 

202.7 

122 

87.9 

1  60 

116.4 

198 

145.4 

236 

173-9 

274 

203.5 

I23 

88.7 

161 

117.1 

199 

146.2 

237 

174.6 

275 

204.3 

124 

89.4 

162 

117.9 

200 

146.9 

238 

175-4 

276 

205.1 

I25 

90.1 

163 

118.6 

201 

147-7 

239 

176.2 

277 

205.9 

126 

90.9 

164 

119.4 

202 

148.5 

240 

176.9 

278 

206.7 

127 

91.6 

165 

I2O.2 

203 

149.2 

241 

177.7 

279 

207.5 

128 

92.4 

166 

120-9 

204 

150.0 

242 

178.5 

280 

208.3 

I29 

93-i 

167 

I2I.7 

205 

150.7 

243 

179-3 

28l 

209.1 

I30 

93-8 

1  68 

122-4 

206 

151.5 

244 

180.1 

282 

209.9 

131 

94.6 

169 

123.2 

207 

152.2 

245 

180.8 

283 

210.7 

I32 

95-3 

170 

123.9 

208 

i53-o 

246 

181.6 

284 

211.5 

133 

96.! 

171 

124.7 

209 

153-7 

247 

182.4 

285 

212.3 

134 

96.9 

172 

125.5 

210 

154-5 

248 

183.2 

286 

213.1 

!35 

97.6 

173 

126.2 

211 

155.2 

249 

184.0 

287 

213.9 

136 

98.3 

174 

127.0 

212 

156.0 

250 

184.8 

288 

214.7 

137 

99.1 

175 

127.8 

213 

156.7 

25I 

185.5 

289 

215.5 

1  Principles  and  Practice  of  Agricultural  Analysis,  Vol.  Ill,  pp.  163-165. 


APPENDIX 


207 


TABLE  VI  —  Continued 


Milli- 
grams of 
copper 

Milli- 
grams ol 
lactose 

Milli- 
grams of 
copper 

Milli- 
grams of 
lactose 

Milli- 
grams of 
copper 

Milli- 
grams of 
lactose 

Milli- 
grams of 
copper 

Milli- 
grams of 
lactose 

Milli- 
grams of 
copper 

Milli- 
grams of 
lactose 

290 

216.3 

312 

233-7 

334 

250.8 

356 

268.8 

378 

287.4 

29I 

2I7.I 

313 

234-5 

335 

251.6 

357 

269.6 

379 

288.2 

292 

217.9 

314 

235-3 

336 

252.5 

358 

270.4 

380 

289.1 

293 

218.7 

315 

236.1 

337 

253-3 

359 

271.2 

381 

289.9 

294 

219.5 

316 

236.8 

338 

254.1 

360 

272.1 

382 

290.8 

295 

220-3 

317 

237.6 

339 

254.9 

361 

272.9 

383 

291.7 

296 

221.  1 

318 

238.4 

340 

255-7 

362 

273-7 

384 

292.5 

297 

221.9 

319 

239.2 

34i 

256.5 

363 

274.5 

385 

293-4 

298 

222.7 

320 

240.0 

342 

257.4 

364 

275-3 

386 

294.2 

299 

223.5 

32I 

240.7 

343 

258.2 

365 

276.2 

387 

295.1 

300 
301 

224.4 
225.2 

322 
323 

241.5 
242.3 

344 
345 

259.0 
259.8 

366 
367 

277.1 
277.9 

388 
389 

296.0 
296.8 

302 

225.9 

324 

243.1 

346 

260.6 

368 

278.8 

39° 

297.7 

o/^Q    r 

303 

226.7 

325 

243-9 

347 

261.4 

369 

279.6 

39  l 

295.5 

3°4 

227.5 

326 

244.6 

348 

262.3 

370 

280.5 

VM 

300  \ 

305 

228.3 

327 

245.4 

349 

263.1 

37i 

281.4 

394 

301.1 

306 

229.1 

328 

246.2 

350 

263.9 

372 

282.2 

395 

302.0 

307 

229.8 

329 

247.0 

351 

264.7 

373 

283.1 

396 

302.8 

308 

230.6 

330 

247.7 

352 

265.5 

374 

283.9 

397 

303-7 

309 

231.4 

331 

248.5 

353 

266.3 

375 

284.8 

398 

304.6 

3IO 

232.2 

332 

249.2 

354 

267.2 

376 

285.7 

399 

305-4 

3" 

232.9 

333 

250.0 

355 

268.0 

377 

286.5 

400 

306.3 

TABLE   VII 
DETERMINATION  OF  DEXTROSE  BY  ALLIHN'S  METHOD1 


Milli- 
grams of 
copper 

Milli- 
grams of 
dextrose 

Milli- 
grams of 
copper 

Milli- 
grams of 
dextrose 

Milli- 
grams of 
copper 

Milli- 
grams of 
dextrose 

Milli- 
grams of 
copper 

Milli- 
grams of 
dextrose 

Milli- 
grams of 
copper 

Milli- 
grams of 
dextrose 

10 

6.1 

19 

10.5 

28 

15.0 

37 

19.4 

46 

23-9 

II 

6.6 

20 

II.O 

29 

15-5 

38 

I9.9 

47 

24.4 

12 

7-i 

21 

II.5 

30 

16.0 

39 

20-4 

48 

24.9 

13 

7.6 

22 

12.0 

31 

16.5 

40 

20.9 

49 

25.4 

H 

8.1 

23 

12.5 

32 

17.0 

4i 

21.4 

50 

25.9 

15 

8.6 

24 

13-0 

33 

17-5 

42 

21.9 

5i 

26.4 

16 

9.0 

25 

13-5 

34 

18.0 

43 

22.4 

52 

26.9 

17 

9-5 

26 

14.0 

35 

18.5 

44 

22.9 

53 

27-4 

18 

IO.O 

27 

14.5 

36 

18.9 

45 

23.4 

54 

27-9 

1  Principles  and  Practice  of  Agricultural  Analysis^  Vol.  Ill,  pp.  156-158. 


208 


QUANTITATIVE  ANALYSIS 


TABLE   VII  —  Continued 


Milli- 
grams  of 
copper 

Milli- 
grams of 
dextrose 

Milli- 
grams of 
copper 

Milli- 
grams of 
dextrose 

Milli- 
grams of 
copper 

Milli- 
grams of 
dextrose 

Milli- 
grams  of 
copper 

Milli- 
grams of 
dextrose 

Milli- 
grams of 
copper 

Milli- 
grams of 
dextrose 

55 

28.4 

96 

48.9 

137 

69.8 

I78 

9I.I 

2I9 

II2.7 

56 

28.8 

97 

49-4 

138 

70.3 

179 

91.6 

220 

II3.2 

57 

29-3 

98 

49.9 

139 

70.8 

1  80 

92.1 

221 

II3-7 

58 

29.8 

99 

50.4 

140 

71-3 

181 

92.6 

222 

II4-3 

59 

30-3 

100 

50.9 

141 

71.8 

182 

93-i 

223 

II4.8 

60 

30.8 

101 

51.4 

142 

72-3 

183 

93-7 

224 

H5.3 

61 

31-3 

102 

51.9 

143 

72.9 

184 

94-2 

225 

II5.9 

62 

31-8 

103 

52.4 

144 

73-4 

185 

94-7 

226 

Il6.4 

63 

32.3 

104 

52.9 

145 

73-9 

1  86 

95.2 

227 

116.9 

64 

32-8 

I05 

53-5 

146 

74-4 

187 

95-7 

228 

H74 

65 

33-3 

1  06 

54.0 

147 

74-9 

188 

96-3 

229 

II8.0 

66 

33-8 

107 

54-5 

148 

75-5 

189 

96.8 

230 

II8.5 

67 

34-3 

108 

55.0 

149 

76.0 

190 

97-3 

231 

Iig.O 

68 

34-8 

109 

55-5 

I50 

76.5 

191 

97.8 

232 

II9.6 

69 

35-3 

no 

56.0 

151 

77.0 

192 

98-4 

233 

120.  1 

70 

35-8 

III 

56.5 

I52 

77-5 

193 

98.9 

234 

120-7 

7i 

36.3 

112 

57.0 

153 

78.1 

194 

99-4 

235 

121.  2 

72 

36.8 

H3 

57-5 

154 

78.6 

195 

100.  0 

236 

I2I.7 

73 

37-3 

114 

58.0 

155 

79.1 

196 

100.5 

237 

122.3 

74 

37-8 

II5 

58.6. 

I56 

79.6 

197 

IOI.O 

238 

122.8 

75 

38.3 

116 

59.1 

157 

80.  i 

198 

101.5 

239 

123.4 

76 

38.8 

117 

59.6 

I58 

80.7 

199 

102.0 

240 

123.9 

77 

39-3 

118 

60.  i 

J59 

81.2 

200 

102.6 

241 

1244 

78 

39-8 

119 

60.6 

1  60 

81.7 

201 

103.1 

242 

125.0 

79 

40-3 

120 

61.1 

161 

82.2 

2O2 

103.7 

243 

125.5 

80 

40.8 

121 

61.6 

162 

82.7 

203 

104.2 

244 

126.0 

81 

41-3 

122 

62.1 

163 

83-3 

204 

104.7 

245 

126.6 

82 

41.8 

123 

62.6 

164 

83.8 

205 

105-3 

246 

I27.I 

83 

42.3 

124 

63.1 

165 

84-3 

206 

105.8 

247 

127.6 

84 

42.8 

I25 

63-7 

1  66 

84.8 

207 

106.3 

248 

I28.I 

85 

43-4 

126 

64.2 

167 

85-3 

208 

106.8 

249 

128.7 

86 

43-9 

127 

64.7 

1  68 

85.9 

209 

107.4 

250 

129.2 

87 

44-4 

128 

65.2 

169 

86.4 

210 

107.9 

251 

129.7 

88 

449 

I29 

65.7 

170 

86.9 

211 

108.4 

252 

130.3 

89 

45-4 

1.30 

66.2 

171 

87.4 

212 

109.0 

253 

130.8 

90 

45-9 

131 

66.7 

172 

87.9 

213 

109.5 

254 

I3I-4 

9i 

46.4 

132 

67.2 

173 

88.5 

214 

IIO.O 

255 

I31'9 

92 

46.9 

133 

67.7 

174 

89.0 

215 

no.  6 

256 

132.4 

93 

47-4 

134 

68.2 

r75 

89.5 

216 

in.  i 

257 

133-0 

94 

47-9 

135 

68.8 

176 

90.0 

217 

in.  6 

258 

133-5 

95 

48.4 

136 

69.3 

177 

90.5 

218 

112.  1 

259 

I34-I 

APPENDIX 


209 


TABLE   VII  —  Continued 


Milli- 
grams  of 
copper 

Milli- 
grams of 
dextrose 

Milli- 
grams of 
copper 

Milli- 
grams of 
dextrose 

Milli- 
grams of 
copper 

Milli- 
grams of 
dextrose 

Milli- 
grams of 
copper 

Milli- 
grams ol 
dextrose 

Milli- 
grams of 
copper 

Milli- 
grams of 
dextrose 

260 

134.6 

301 

I57.I 

342 

I79.8 

383 

203.1 

424 

226.9 

26l 

I35-I 

302 

157.6 

343 

180.4 

384 

203.7 

425 

227.5 

262 

135-7 

303 

158.2 

344 

180.9 

385 

204.3 

426 

228.0 

263 

136.2 

304 

158.7 

345 

I8I.5 

386 

204-8 

427 

228.6 

264 

136.8 

305 

159.3 

346 

I82.I 

387 

205.4 

428 

229.2 

265 

137-3 

306 

159.8 

347 

182.6 

388 

206.0 

429 

229.8 

266 

137-8 

3°7 

160.4 

348 

183.2 

389 

206.5 

43° 

230.4 

267 

138.4 

308 

160.9 

349 

183.7 

390 

207.1 

43i 

231.0 

268 

138.9 

3°9 

161.5 

350 

184.3 

391 

207.7 

432 

231.6 

269 

:39-5 

3IO 

162.0 

35i 

184.9 

392 

208.3 

433 

232.2 

270 

140.0 

311 

162.6 

352 

185.4 

393 

208.8 

434 

232.8 

271 

140.6 

3I2 

I63.I 

353 

186.0 

394 

209.4 

435 

233.4 

272 

141.1 

313 

163.7 

354 

186.6 

395 

210.0 

436 

233-9 

273 

141.7 

3H 

164.2 

355 

187.2 

396 

210.6 

437 

234-5 

274 

142.2 

315 

164.8 

356 

187.7 

397 

211.  2 

438 

235-1 

275 

142.8 

316 

165.3 

357 

188.3 

398 

2II-7 

439 

2357 

276 

H3-3 

317 

165.9 

358 

188.9 

399 

212.3 

440 

236.3 

277 

143-9 

318 

166.4 

359 

189.4 

400 

212.9 

441 

236.9 

278 

144.4 

319 

167.0 

360 

190.0 

401 

213.5 

442 

237.5 

279 

145.0 

320 

167.5 

36i 

190.6 

402 

2I4.I 

443 

238.1 

280 

145-5 

32I 

I68.I 

362 

191.1 

403 

214.6 

444 

238.7 

28l 

146.1 

322 

168.6 

363 

191.7 

404 

215.2 

445 

239-3 

282 

146.6 

.323 

169.2 

364 

192.3 

405 

215.8 

446 

239.8 

283 

147.2 

324 

169.7 

365 

192.9 

406 

2l6.4 

447 

240.4 

284 

147-7 

325 

170.3 

366 

193-4 

407 

217.0 

448 

241.0 

285 

148.3 

326 

170.9 

367 

194.0 

408 

217.5 

449 

241.6 

286 

148.8 

327 

I7I.4 

368 

194.6 

409 

2I8.I 

450 

242.2 

287 

149.4 

328 

172.0 

369 

195.1 

410 

218.7 

45i 

242.8 

288 

149.9 

329 

172.5 

370 

195-7 

411 

219.3 

452 

2434 

289 

I50-5 

330 

I73-I 

37i 

196.3 

412 

219.9 

453 

244.0 

290 

151.0 

331 

1737 

372 

196.8 

4i3 

220-4 

454 

244.6 

29I 

151.6 

332 

174.2 

373 

197.4 

414 

221.0 

455 

245.2 

292 

152.1 

333 

174.8 

374 

198.0 

4i5 

221.6 

456 

245.7 

293 

152.7 

334 

175-3 

375 

198.6 

416 

222.2 

457 

246.3 

294 

153-2 

335 

'75-9 

376 

199.1 

4i7 

222.8 

458 

246.9 

295 

153.8 

336 

176.5 

377 

199.7 

418 

223.3 

459 

247.5 

296 

154.3 

337 

177.0 

378 

200.3 

419 

223.9 

460 

248.1 

297 

154.9 

338 

177.6 

379 

200.8 

420 

224.5 

461 

248.7 

298 

1554 

339 

178.1 

380 

201.4 

421 

225.1 

462 

249-3 

299 

156.0 

340 

178.7 

38i 

202.0 

422 

225.7 

463 

249.9 

300 

156.5 

34i 

179-3 

382 

202.5 

423 

226.3 

2IO 


QUANTITATIVE  ANALYSIS 


TABLE  VIII 
LOGARITHMS 


NATURAL 
NUMBERS 

0 

1 

2 

8 

4 

5 

6 

7 

8 

9 

PROPORTIONAL  PART 

1 

» 

-•5 

4 

r> 

« 

7  8 

IO 

0000 

0043 

0086 

0128 

0170 

0212 

0253 

0294 

0334 

0374 

4 

8 

12 

17 

21 

25 

2933 

II 

0414 

0453 

0492 

0531 

0569 

0607 

0645 

0682 

0719 

0755 

4 

8 

XX 

15 

19 

23 

26  30 

12 

0792 

0828 

0864 

0899 

0934 

0969 

1004 

1038 

1072 

1106 

3 

7 

IO 

14 

I7 

21 

24  28 

13 

1139 

1173 

1206 

1239 

1271 

1335 

1367 

1399 

1430 

3 

6 

IO 

1  6 

19 

2326 

14 

1461 

1492 

1523 

1553 

1584 

1614 

1644 

1673 

1703 

1732 

3 

6 

9 

2 

15 

18 

21  24 

15 

1761 

1790 

1818 

1847 

1875 

1903 

1931 

1959 

1987 

2014 

3 

6 

8 

I 

14 

I7 

20  22 

16 

2041 

2068 

2095 

2122 

2148 

2175 

22OI 

2227 

2253 

2279 

3 

5 

8 

I 

13 

x6 

l82I 

17 

2304 

2330 

2355 

2380 

2405 

2430 

2455 

2480 

2504 

2529 

2 

5 

7 

O 

12 

15 

17  20 

18 

2553 

2577 

2601 

2625 

2648 

2b72 

2695 

2718 

2742 

2765 

2 

5 

7 

9 

12 

14 

16  19 

19 

2788 

2810 

2833 

2856 

2878 

2900 

2923 

2945 

2967 

2989 

2 

4 

7 

9 

II 

«3 

16  18 

20 

3010 

3032 

3054 

3075 

3096 

3118 

3139 

3160 

3181 

3201 

2 

4 

6 

8 

II 

13 

15  17 

21 

3222 

3243 

3263 

3284 

3304 

3324 

3345 

3365 

3385 

3404 

2 

4 

6 

8 

IO 

12 

14  16 

22 

3424 

3444 

3464 

3483 

3502 

3522 

354i 

356° 

3579 

3598 

2 

4 

6 

8 

ro 

xa 

14  15 

23 

3617 

3636 

3655 

3674 

3692 

3711 

3729 

3747 

3766 

3784 

2 

4 

6 

7 

9 

XX 

13  T5 

24 

3802 

3820 

3838 

3856 

3874 

3892 

3909 

3927 

3945 

3962 

2 

4 

5 

7 

9 

ii 

12  14 

25 

3979 

3997 

4014 

4031 

4048 

4065 

4082 

4099 

4116 

4133 

2 

3 

5 

7 

9 

xo 

12  14 

26 

415° 

4166 

4183 

42OO 

4216 

4232 

4249 

4265 

4281 

4298 

2 

3 

5 

7 

8 

xo 

II  13 

27 

43H 

4330 

4346 

4362 

4378 

4393 

4409 

4425 

444° 

445  6 

2 

3 

5 

6 

8 

9 

II  13 

28 

4472 

4487 

4502 

4518 

4533 

4548 

45  64 

4579 

4594 

4609 

2 

3 

5 

6 

8 

9 

II  12' 

29 

4624 

4639 

4654 

4669 

4683 

4698 

47*3 

4728 

4742 

4757 

I 

3 

4 

6 

7 

9 

j 
10  12 

30 

4771 

4786 

4800 

4814 

4829 

4843 

4857 

4871 

4886 

4900 

I 

3 

4 

6 

7 

9 

10  11 

31 

4914 

4928 

4942 

4955 

4969 

4983 

4997 

5011 

5024 

5038 

I 

3 

4 

6 

7 

8 

10  x" 

32 

5051 

5065 

5°79 

5092 

5105 

5119 

5132 

5*45 

5159 

5172 

I 

3 

4 

5 

7 

8 

33 

5185 

5198 

5211 

5224 

5237 

525° 

5263 

5276 

5289 

53°2 

I 

3 

4 

5 

6 

8 

9  10 

34 

5315 

5328 

5340 

5353 

5366 

5378 

5391 

5403 

5428 

I 

3 

4 

5 

6 

8 

910 

35 

5441 

5453 

5465 

5478 

5490 

5502 

55'4 

5527 

5539 

5551 

I 

a 

4 

5 

6 

7 

9  10 

36 

5563 

5575 

5587 

5599 

561  1 

5623 

5635 

5647 

5658 

5670 

X 

.a 

4 

5 

6 

7 

8  10 

37 

5682 

5694 

5705 

5717 

5729 

5740 

5752 

5763 

5775 

5786 

I 

a 

3 

5 

6 

7 

8  9 

38 

5798 

5809 

5821 

5832 

5843 

5855 

5866 

5877 

5888 

5899 

I 

a 

3 

5 

6 

7 

8  9 

39 

59" 

5922 

5933 

5944 

5955 

5966 

5977 

5988 

5999 

6010 

I 

2 

3 

4 

5 

7 

8  9 

40 

6021 

6031 

6042 

6053 

6064 

6075 

6085 

6096 

6107 

6117 

X 

2 

3 

4 

5 

6 

8  9 

41 

6128 

6138 

6149 

6160 

6170 

6180 

6191 

6201 

6212 

6222 

x 

2 

3 

4 

5 

6 

7  8 

42 

6232 

6243 

6253 

6263 

6274 

6284 

6294 

6304 

6314 

6325 

X 

2 

;; 

4 

5 

6 

7  8 

43 

6335 

6345 

6355 

6365 

6375 

6385 

6395 

6405 

6415 

6425 

I 

2 

3 

4 

5 

6 

7  8 

44 

6435 

6444 

6454 

6464 

6474 

6484 

6493 

6503 

65J3 

6522 

I 

2 

3 

4 

5 

6 

7  8 

45 

6532 

6542 

6551 

6561 

6571 

6580 

6590 

6599 

6609 

6618 

X 

2 

3 

4 

5 

6 

7  8 

46 

6628 

6637 

6646 

6656 

6665 

6675 

6684 

6693 

6702 

6712 

I 

2 

3 

4 

3 

6 

7  7 

47 

6721 

6730 

6739 

6749 

6758 

6767 

6776 

6785 

6794 

6803 

x 

2 

3 

4 

5 

5 

6  7 

48 

6812 

6821 

6830 

6839 

6848 

6857 

6866 

6875 

6884 

6893 

x 

2 

3 

4 

4 

5 

6  7 

49 

6902 

6911 

6920 

6928 

6937 

6946 

6955 

6964 

6972 

6981 

I 

2 

3 

4 

4 

5 

6  7 

50 

6990 

6998 

7007 

7016 

7024 

7°33 

7042 

7050 

7°59 

7067 

I 

2 

3 

3 

4 

5 

6  7 

51 

7076 

7084 

7°93 

7101 

7110 

7118 

7126 

7J35 

7*43 

7152 

x 

2 

3 

3 

4 

5 

6  7 

52 

7160 

7168 

7177 

7185 

7193 

7202 

7210 

7218 

7226 

7235 

X 

2 

2 

3 

4 

5 

6  7 

53 

7243 

7251 

7259 

7267 

7275 

7284 

7292 

7300 

7308 

73'6 

t 

3 

a 

3 

4 

5 

6  6 

54 

7324 

7332 

7340 

7348 

7356 

7364 

7372 

7380 

7388 

7396 

X 

3 

2 

3 

4 

5 

6  6 

APPENDIX 


211 


TABLE   Mill  — Continued 


NATURAL 
NUMBERS 

0 

1 

2 

8 

4 

5 

6 

7 

8 

9 

PROPORTIONAL  PARTS 

1 

3 

3 

4 

5 

6 

7  8 

55 

7404 

7412 

74i9 

7427 

7435 

7443 

745  i 

7459 

7466 

7474 

3 

4 

5 

5  6 

56 

57 

7482 
7559 

74?A 
7566 

7497 
7574 

75°5 
7582 

75*3 
7589 

7520 
7597 

7528 
7604 

7536 
7612 

7543 
7619 

7551 
7627 

3 
3 

4 
4 

5 
5 

5  6 
5  6 

58 

'  **.*>  •* 

7634 

7642 

7649 

7657 

7664 

7672 

7679 

7686 

7694 

7701 

3 

4 

4 

5  6 

59 

7709 

77l6 

7723 

773i 

7738 

7745 

7752 

7760 

7767 

7774 

3 

4 

4 

5  6 

60 

7782 

7789 

7796 

7803 

7810 

7818 

7825 

7832 

7839 

7846 

3 

4 

4 

5  6 

61 

7853 

7860 

7868 

7875 

7882 

7889 

7896 

7903 

7910 

7917 

3 

4 

4 

5  6 

62 

7924 

793  * 

7938 

7945 

7952 

7959 

7966 

7973 

7980 

7987 

3 

3 

4 

5  6 

63 

7993 

8000 

8007 

8014 

8021 

8028 

8035 

8041 

8048 

8055 

3 

3 

4 

5  5 

64 

8062 

8069 

8075 

8082 

8089 

8096 

8102 

8109 

8116 

8122 

3 

3 

4 

5  5 

65 

8129 

8136 

8142 

8149 

8156 

8162 

8169 

8176 

8182 

8189 

3 

3 

4 

5  5 

66 

8i95 

8202 

8209 

8215 

8222 

8228 

8235 

8241 

8248 

8254 

3 

3 

4 

5  5 

67 

8261 

8267 

8274 

8280 

8287 

8293 

8299 

8306 

8312 

8319 

3 

3 

4 

5  5 

68 

8325 

8331 

8338 

8344 

835  i 

8357 

8363 

8370 

8376 

8382 

3 

3 

4 

4  5 

69 

8388 

8395 

8401 

8407 

8414 

8420 

8426 

8432 

8439 

8445 

2 

3 

4 

4  5 

70 

845  r 

8457 

8463 

8470 

8476 

8482 

8488 

8494 

8500 

8506 

2 

3 

4 

4  5 

71 

85U 

8519 

8525 

8531 

8537 

8543 

8549 

8555 

8561 

8567 

2 

3 

4 

4  5 

72 

8573 

8579 

8585 

8591 

8597 

8603 

8609 

8615 

8621 

8627 

•2 

3 

4 

4  5 

73 

8633 

8639 

8645 

8651 

8657 

8663 

8669 

8675 

8681 

8686 

2 

3 

4 

4  5 

74 

8692 

8698 

8704 

8710 

8716 

8722 

8727 

8733 

8739 

8745 

9 

3 

4 

4  5 

75 

8751 

8756 

8762 

8768 

8774 

8779 

8785 

8791 

8797 

8802 

•2 

3 

3 

4  5 

76 

8808 

8814 

8820 

8825 

8831 

8837 

8842 

8848 

8854 

8859 

a 

3 

3 

4  5 

77 

8865 

8871 

8876 

8882 

8887 

8893 

8899 

8904 

8910 

8915 

2 

3 

3 

4  4 

78 

8921 

8927 

8932 

8938 

8943 

8949 

8954 

8960 

8965 

8971 

2 

3 

3 

4  4 

79 

8976 

8982 

8987 

8993 

8998 

9004 

9009 

9015 

9020 

9025 

2 

3 

3 

4  4 

80 

9031 

9036 

9042 

9047 

9053 

9058 

9063 

9069 

9074 

9079 

2 

3 

3 

4  4 

81 

9085 

9090 

9096 

9101 

9106 

9112 

9117 

9122 

9128 

9133 

2 

3 

3 

4  4 

82 

9138 

9H3 

9149 

9*54 

9i59 

9165 

9170 

9175 

9180 

9186 

2 

3 

3 

4  4 

83 

9191 

9196 

9201 

9206 

9212 

9217 

9222 

9227 

9232 

9238 

2 

3 

3 

4  4 

84 

9243 

9248 

9253 

9258 

9263 

9269 

9274 

9279 

9284 

9289 

2 

3 

3 

4  4 

85 

9294 

9299 

9304 

9309 

93i5 

9320 

9325 

9330 

9335 

9340 

2 

3 

3 

4  4 

86 

9345 

9350 

9355 

9360 

9365 

937° 

9375 

9380 

9385 

9390 

2 

3 

3 

4  4 

87 

9395 

9400 

9405 

9410 

94i5 

9420 

9425 

943° 

9435 

9440 

a 

2 

3 

3  4 

88 

9445 

945° 

9455 

9460 

9465 

9469 

9474 

9479 

9484 

9489 

0 

2 

2 

3 

3  4 

89 

9494 

9499 

95°4 

95°9 

95J3 

95i8 

9523 

9528 

9533 

9538 

o 

2 

2 

3 

3  4 

90 

9542 

9547 

9552 

9557 

9^62 

9S66 

9571 

9576 

958i 

9586 

o 

2 

2 

3 

3  4 

9i 

9590 

9595 

9600 

9605 

9609 

9614 

9619 

9624 

9628 

9633 

0 

2 

2 

3 

3  4 

92 

(\1 

9638 
068  c 

9643 
0680 

9647 

f\f\c\A 

9652 

(\f\f\C\ 

9657 

9*-r\i 

9661 

CtTlR 

9666 

r\t-i  T  -•> 

9671 

f\hj  T  *7 

9675 

9680 

.-.  ^  -,  >, 

0 

o 

2 

2 

3 

3  4 

yj 
94 

yu°3 
973i 

yuoy 
9736 

yuy4 
9741 

y°yy 
9745 

7UO 

975° 

9/uo 
9754 

97J3 
9759 

9717 
9763 

9722 
9768 

9727 
9773 

0 

2 

2 

3 

3  4 

95 

9777 

9782 

9786 

9791 

9795 

9800 

9805 

9809 

9814 

9818 

0 

2 

2 

3 

3  4 

96 

9823 

9827 

9832 

9836 

9841 

9845 

9850 

9854 

9859 

9863 

o 

2 

2 

3 

3  4 

97 

9868 

9872 

9877 

9881 

9886 

9890 

9894 

9899 

9903 

9908 

o 

2 

2 

3 

3  4 

98 

9912 

9917 

9921 

9926 

993° 

9934 

9939 

9943 

9948 

9952 

o 

2 

2 

3 

3  4 

99 

9956 

9961 

9965 

9969 

9974 

9978 

9983 

9987 

9991 

9996 

0 

2 

2 

3 

3  3 

i 

! 

212 


QUANTITATIVE  ANALYSIS 


TABLE  IX 
ANTILOGARITHMS 


LOGARITHMS 

0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

PROPORTIONAL  PART 

1 

8 

3 

4 

r> 

(> 

7  8 

.00 

IOOO 

1  002 

IOOs 

1007 

1009 

IOI  2 

1014 

1016 

IOIQ 

IO2I 

.01 

1023 

1026 

*-^njj 
1028 

1030 

1033 

!035 

1038 

1040 

IO42 

1045 

o 

o 

i 

i 

2  2 

.02 

1047 

1050 

1052 

1054 

1057 

1059 

1062 

1064 

1067 

1069 

O 

0 

i 

i 

2   2 

•03 

1072 

1074 

1076 

1079 

1081 

1084 

1086 

1089 

1091 

I094 

0 

o 

i 

i 

2  2 

.04 

1096 

1099 

1  102 

1104 

1107 

1109 

III2 

1114 

III7 

III9 

0 

X 

X 

2 

2  2 

•°5 

1  122 

1125 

II27 

1130 

1132 

"35 

1138 

1140 

H43 

1146 

o 

x 

2 

2  2 

.06 

i  ij.8 

iim 

II  r  ? 

ii  c6 

1  1  cq 

1161 

1164 

1  167 

1  169 

1  1  72 

.07 

*  **^*-' 

"75 

D* 
1178 

*  j  J 

1180 

j.  i^u 
1183 

•*  *  jy 

1186 

1189 

II9I 

1194 

1197 

11  /•* 

1199 

o 

X 

2 

2  2 

.08 

1202 

1205 

1208 

I2II 

1213 

1216 

1219 

1222 

I225 

I227 

o 

I 

a 

2   2 

.09 

1230 

1233 

1236 

1239 

1242 

1245 

1247 

1250 

1253 

1256 

0 

X 

2 

2  2 

.10 

1259 

1262 

1265 

1268 

1271 

1274 

1276 

1279 

1282 

1285 

o 

I 

2 

2  2 

.11 

1288 

1291 

1294 

1297 

1300 

1303 

1306 

1309 

I3I2 

1315 

o 

2 

2 

2  2 

.12 

I3l8 

1321 

1324 

1327 

1330 

1334 

1337 

1340 

J343 

J346 

o 

2 

2 

2  2 

•13 

1349 

1352 

1355 

1358 

1361 

1365 

1368 

1371 

'374 

!377 

0 

a 

2 

2  3 

.14 

1380 

i3«4 

1387 

1390 

1393 

1396 

1400 

1403 

1406 

1409 

0 

2 

2 

2  3 

.15 

1413 

1416 

1419 

1422 

1426 

1429 

1432 

H35 

*439 

1442 

o 

2 

2 

2  3 

.16 

1445 

1449 

H52 

H55 

1459 

1462 

1466 

1469 

1472 

1476 

o 

2 

2 

2   3 

.17 

H79 

1483 

1486 

1489 

H93 

1496 

1500 

I5°3 

i5°7 

1510 

0 

2 

2 

2  3 

.18 

I5H 

i5'7 

1521 

1524 

1528 

i53i 

1535 

1538 

1542 

J545 

0 

2 

2 

2  3 

.19 

1549 

1552 

1556 

1560 

1563 

1567 

IS7° 

1574 

1578 

1581 

0 

2 

2 

3  3 

.20 

1585 

1589 

1592 

1596 

1600 

1603 

1607 

1611 

1614 

1618 

0 

2 

a 

3  3 

.21 

1622 

1626 

1629 

1633 

1637 

1641 

1644 

1648 

1652 

1656 

0 

2 

2 

3  3 

.22 

1660 

1663 

1667 

1671 

1675 

1679 

1683 

1687 

1690 

1694 

0 

2 

2 

3  3 

•23 

1698 

1702 

1706 

1710 

1714 

1718 

1722 

1726 

1730 

1734 

o 

2 

a 

3  3 

.24 

1738 

1742 

1746 

175° 

*754 

1758 

1762 

1766 

1770 

*774 

o 

2 

a 

3  3 

•25 

1778 

1782 

1786 

1791 

!795 

1799 

1803 

1807 

1811 

1816 

0 

2 

a 

3  3 

.26 

1820 

1824 

1828 

1832 

1837 

1841 

1845 

1849 

1854 

1858 

o 

2 

3 

3  3 

.27 

1862 

1866 

1871 

1875 

1879 

1884 

1888 

1892 

1897 

1901 

o 

2 

3 

3  3 

.28 

1905 

1910 

1914 

1919 

1923 

1928 

1932 

1936 

1941 

1945 

o 

2 

3 

3  4 

.29 

195° 

1954 

1959 

1963 

1968 

1972 

1977 

1982 

1986 

1991 

o 

a 

3 

3  4 

•30 

1995 

2OOO 

2004 

2OO9 

2014 

2018 

2023 

2028 

2032 

2037 

0 

2 

3 

3  4 

•31 

2042 

2046 

2051 

2056 

2061 

2065 

2070 

2075 

2080 

2084 

o 

a 

3 

3  4 

•32 

2089 

2094 

2099 

2104 

2109 

2113 

2118 

2123 

2128 

2133 

o 

2 

3 

3  4 

•33 

2138 

2143 

2148 

2153 

2158 

2163 

2168 

2173 

2178 

2183 

o 

2 

3 

3  4 

•34 

2188 

2193 

2198 

22O3 

2208 

2213 

2218 

2223 

2228 

2234 

x 

3 

3 

4  4 

•35 

2239 

2244 

2249 

2254 

2259 

2265 

2270 

2275 

2280 

2286 

,x 

3 

3 

4  4 

•36 

2291 

2296 

2301 

2307 

2312 

2317 

2323 

2328 

2333 

2339 

I 

3 

3 

4  4 

•37 

2344 

2350 

2355 

2360 

2366 

2371 

2377 

2382 

2388 

2393 

X 

3 

3 

4  4 

•38 

2399 

2404 

2410 

2415 

2421 

2427 

2432 

2438 

2443 

2449 

X 

3 

3 

4  4 

•39 

2455 

2460 

2466 

2472 

2477 

2483 

2489 

2495 

2500 

2506 

X 

3 

3 

4  5 

.40 

2512 

2518 

2523 

2529 

2535 

2541 

2547 

2553 

2559 

2564 

X 

3 

4 

4  5 

.41 

2570 

2576 

2582 

2588 

2594 

2600 

2606 

2612 

2618 

2624 

X 

3 

4 

4  5 

.42 

2630 

2636 

2642 

2649 

2655 

2661 

2667 

2673 

2679 

2685 

I 

3 

4 

4  5 

•43 

2692 

2698 

2704 

2710 

2716 

2723 

2729 

2735 

2742 

2748 

I 

3 

3 

4 

4  5 

•44 

2754 

2761 

2767 

2773 

2780 

2786 

2793 

2799 

2805 

2812 

I 

3 

3 

4 

4  5 

•45 

2818 

2825 

2831 

2838 

2844 

2851 

2858 

2864 

2871 

2877 

I 

3 

3 

4 

5  5 

.46 

2884 

2891 

2897 

2904 

2911 

2917 

2924 

2931 

2938 

2944 

I 

3 

3 

4 

5  5 

•47 

295  * 

2958 

2965 

2972 

2979 

2985 

2992 

2999 

3006 

3013 

I 

3 

3 

4 

5  5 

.48 

3020 

3027 

3034 

3041 

3048 

3055 

3062 

3069 

3076 

3083 

I 

3 

4 

4 

5  6 

•49 

3090 

3°97 

3I05 

3112 

3H9 

3126 

3133 

3*41 

3H8 

3155 

I 

3 

4 

4 

5U 

APPENDIX 


213 


TABLE   IX  — Continued 


LOGARITHMS 

0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

PROPORTIONAL  PARTS 

1 

2 

3 

4 

5 

G 

7 

8 

•5° 

3162 

3*7° 

3»77 

3184 

3192 

3199 

3206 

3214 

3221 

3228 

3 

4 

4 

5 

6 

•51 

3236 

3243 

3251 

3258 

3266 

3273 

3281 

3289 

3296 

33°4 

3 

4 

5 

5 

6 

•52 

33ii 

33'9 

3327 

3334 

3342 

335° 

3357 

3365 

3373 

338i 

3 

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3388 

3396 

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3420 

3428 

3436 

3443 

345  J 

3459 

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4 

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6 

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3467 

3475 

3483 

3491 

3499 

3508 

35'6 

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3532 

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3 

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5 

6 

6 

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3548 
3631 

3556 
3639 

3648 

3573 
3656 

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3664 

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3681 

3606 
3690 

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3698 

3622 
3707 

2 

3 

3 
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4 

4 

5 
5 

6 
6 

7 

7 

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37J5 

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3733 

374i 

375° 

3758 

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3 

4 

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3828 

3837 

3846 

3855 

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3873 

3882 

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4 

4 

5 

6 

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3890 

3899 

3908 

3917 

3926 

3936 

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3954 

3963 

3972 

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3990 

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4009 

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4027 

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4055 

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6 

6 

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4074 

4083 

4093 

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4121 

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6 

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4966 

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5000 

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5212 

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12 

13 

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13 

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8222 

8241 

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10 

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8590 

8610 

8630 

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6 

8 

10 

12 

M 

16 

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8770 

8790 

8810 

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8872 

8892 

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6 

8 

10 

12 

14 

16 

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9016 

9036 

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6 

8 

10 

12 

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9120 

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9226 

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7 

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5 

17 

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9572 

9594 

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9638 

9661 

9683 

9705 

9727 

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4 

7 

9 

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13 

6 

18 

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9772 

9795  9817 

9840  |  9863 

9886 

9908 

993i 

9944 

9977 

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7 

9 

11 

14 

6 

18 

214 


QUANTITATIVE  ANALYSIS 

TABLE   X 

COMBINING  AND  ATOMIC  WEIGHTS 
1907 


Aluminium     . 

.    .     .  Al 
.    .    .  Sb 

0  =  16. 

27.1 

I2O  2 

Neodymium   .     . 
Neon 

.     .  Nd 
Ne 

0=16. 
143.6 

Argon  . 

...  A 

Nickel 

Ni 

Arsenic 

...  As 

7C.O 

Nitrogen    . 

.     .  N 

l2t  oi 

Barium 

.    .       Ba 

1  77  4. 

Osmium 

Os 

.     .     .  Bi 

2O8.O 

Oxvsren 

.     .  O 

1  6  oo 

Boron    . 

.     .     .  B 

I  I.O 

Palladium  . 

.     .  Pd 

1  06  c 

Bromine    . 

.     .     .  Br 

7Q.O.6 

Phosphorus 

.     .  P 

Cadmium  . 

.     .     .  Cd 

1  12.4. 

Platinum   .     . 

.     .  Pt 

TQ/1    8 

Caesium     . 

.    .     .  Cs 

Potassium 

K 

Calcium     .     . 

.     .     .  Ca 

4.O  I 

Praseodymium 

.     .  Pr 

I4.O  C 

Carbon      .     . 

.     .     .  C 

12  OO 

Radium 

Rd 

22C 

Cerium       .     . 

.     .     .  Ce 

I4O  2C 

Rhodium             . 

Rh 

IO7  O 

Chlorine 

.    .       Cl 

Rubidium 

Rb 

Chromium 
Cobalt 

.     .     .  Cr 
...  Co 

52.1 

Ruthenium     .     . 
Samarium 

.     .  Ru 
Sa 

IOI-7 

Columbium 

.     .       Cb 

59 

Scandium 

Sc 

4.4.  I 

Copper 

.    «       Cu 

67  6 

Selenium 

Se 

Erbium 

Er 

1  66 

Silicon 

Si 

28  4 

Europium  .     . 

.     .     .  Eu 

I  C2 

Silver         .     .     . 

•  Ag 

IO7.  Q7 

Fluorine    .     .. 

.     .     .  F 

IQ.O 

Sodium 

•"•& 

.     .  Na 

Gadolinium    . 

.     .     .  Gd 

u6 

Strontium  .     .     . 

.     .  Sr 

87.6 

Gallium     . 

.     .     .  Ga 

±  2^1 

7O 

Sulphur     .     .     . 

.     .  S 

72.O6 

Germanium    . 
Glucinum 

.     .     .  Ge 
.     .     .  Gl 

72.5 

9  * 

Tantalum  .     .     . 
Tellurium 

.     .  Ta 
.     .  Te 

181 

127.6 

Gold 

Au 

I  Q7  2 

Terbium 

.     .  Tb 

I  CQ-2 

Helium           • 

.     .       He 

4.  O 

Thallium   .     .     . 

.     .  Tl 

2O4..  I 

Hydrogen 

.     .       H 

I  OO8 

Thorium    .     .     . 

.     .  Th 

272.  C 

Indium 

In 

IIC 

Thulium         .     . 

.     .  Tm 

171 

Iodine 

I 

ii  J 
126  Q7 

Tin                  .     . 

.  Sn 

I  IQ.O 

Iridium 

Ir 

Titanium        .     . 

Ti 

4.8.1 

Iron 

Fe 

93 

Tungsten        . 

.     .  W 

184. 

Krypton 

Kr 

81  8 

Uranium 

.     .  U 

278.  c 

Lanthanum    . 
Lead 

...  La 
Pb 

138.9 
206  9 

Vanadium      .     . 
Xenon        . 

.     .  V 
.     .  Xe 

51.2 
128 

Lithium 

Li 

7  07 

Ytterbium  .     .     . 

.     .  Yb 

177.0 

Magnesium    . 
Manganese 

.     .     .  Mg 
.     .        Mn 

24.36 
p  p  O 

Yttrium      .     .     . 

.     .  Yt 
.     .  Zn 

89.0 

6c.4 

Mercury     •     . 

.  HP 

2OO  O 

Zirconium       .     . 

.     .  Zr 

QO.6 

Molybdenum  . 

iA& 
.     .     .Mo 

96.0 

ANSWERS  TO   PROBLEMS 


1.  Na2CO3. 

2.  K2PtCl6. 

3.  K2CrO4. 

4.  (NH4)2MoO4. 

5.  C4H606. 

6.  Zn      40.51  per  cent. 
ZnO  50.41  per  cent. 

7.  Fe      14.25  per  cent. 
FeO   18.33  Per  cent- 
S        16.35  Per  cent- 
SO3   40.83  per  cent. 
H2O  27.56  per  cent. 

8.  ZnO  53.41  per  cent. 
P2O5  46.59  per  cent. 

9.  CaO  48.15  per  cent. 
SiO2  51.85  per  cent. 

10.  a.   0.8999  gram. 

b.  0.2784  gram. 
0.6376  gram. 

c.  0.4562  gram. 

d.  0.2 1 14  gram. 
'•   °-7357  gram« 
/    I-I397  grams- 

11.  0.5475  gram. 

12.  0.4113  gram. 

13.  0.5412  gram. 

14.  0.6169  gram. 

15.  54.79  per  cent. 

16.  98.02  per  cent. 

17.  11.90  per  cent. 

18.  K      1.93  per  cent. 
Na    4.46  per  cent. 

19.  Ca    0.2257  gram. 
Mg  0.1840  gram. 

20.  PbO  1.0637  grams. 
BaO  0.5613  gram. 


21.  8.98  per  cent. 

22.  3.06  c.c. 

23.  165.83  c.c. 

24.  3.04  c.c. 

25.  4.30  c.c. 

26.  91.87  per  cent. 

27.  96.23  per  cent. 

28.  99.93  per  cent. 

29.  Na2O      61.70  per  cent. 
NaOH   47.07  per  cent. 
Na2COs  43.06  per  cent. 

30.  14.47  per  cent. 

31.  69.43  per  cent. 

32.  22.74  per  cent. 

33.  29.59  per  cent. 

34.  2.27  c.c. 

35.  Normal. 

36.  0.9778  Normal. 

37.  666.5  grams. 

38.  13.66  per  cent. 

39.  a.   0.001256  gram;   11.370.0. 

b.  0.001249  gram>    11.46  c.c. 

c.  0.001259  gram;    11.370.0. 

40.  99.61  per  cent. 

41.  99.63  per  cent. 

42.  CaO  50.43  per  cent. 

43.  a.   0.0007943  gram;    18.02  c.c. 
b.   0.0007966  gram;    17.97  c.c. 

44.  a.    0.0138    gram    of    Oxygen 

per  c.c. 
b.   2.93  per  cent  H2O2. 

45.  0.01061  gram. 

46.  a.   0.01230  gram. 

b.   0.09687  Normality  Factor. 

47.  24.48  per  cent. 


2I5 


216 


ANSWERS 


48.  67.25  per  cent. 

49.  0.01051  gram. 

0.08275  Normality  Factor. 

50.  0.4120  gram. 

51.  0.3285  gram. 

52.  0.5259  gram. 

53.  0.4378  gram. 

54.  K2SO4    0.3543  gram. 
Na2SC>4  0.7457  gram. 

55.  For  o.i  per  centP,  0.2784  gram. 
For  0.2  per  cent  P2Os,  0.3195  gram. 

56.  4.46  c.c. 

57.  FeO     2.66  per  cent. 
A12O3  14.89  per  cent. 
P          0.501  per  cent. 

58.  81.85  per  cent. 

59.  0.1045  gram- 

60.  674.7  c.c. 

61.  5.65  c.c. 

62.  1.15  c.c. 

63.  a.    15.45  grams. 
b.    3016.5  c.c. 


64.  1.226  Normality  Factor. 

65.  a.  0.1534  Normality  Factor. 
b.   0.3851  gram. 

66.  5.21  per  cent. 

67.  43.23  per  cent. 

68.  14.95  Reichert-Meissl  Number. 

69.  206.0  Saponification  Number. 

70.  1.83  per  cent. 

71.  26.05  Per  cent. 

72.  87.50  per  cent. 

73.  o.i 6  per  cent  too  low. 

74.  0.000252  gram  per  c.c. 

75.  0.5018  gram. 

76.  1039.6  c.c. 

77.  a.  28.21  per  cent. 
b.    22.289  grams. 

78.  a.  44.54  per  cent. 
b.   0.5724  gram  Fe. 

0.6453  gram  Oxalic  Acid. 

79.  35-35  Iodine  Absorption  Number. 

80.  0.1145  gram. 


INDEX 


Acidimetry,  51. 

Acids,  specific  gravity,  tables  of,  203. 

Adams  paper  coil  method  for  fat  in  milk, 

88. 

Alkalimetry,  51. 

Allihn's  method  for  carbohydrates,  124. 
Aluminium,  determination  of,  37. 

in  soils,  150. 

Ammonia,  specific  gravity,  tables  of,  205. 
Answers  to  problems,  215-216. 
Antilogarithms,  table  of,  212-213. 
Available  oxygen,  65. 

Babcock  method  for  fat  in  milk,  90. 
Balance,  16-20. 

exercises  with,  22-23. 
Balancing  equations,  178. 
Bleaching  powder,  estimation  of  available 

chlorine  in,  82. 
Books  of  reference,  195. 
Bumping,  9,  156. 
Butter,  analysis  of,  100-118. 

Calcium,  determination  of,  32,  73,  152. 

separation  from  magnesium,  33. 
Calibration,  of  burettes,  45. 

curve,  48. 

Carbohydrates  in  cereals,  120,  123. 
Carbon  dioxide,  determination  of,  156. 
Caustic  alkali,  determination  of,  66. 
Cereals,  119. 

Chlorine,  determination  of,  24/82,  102. 
Clerget's  inversion  method  for  sucrose,  124. 
Crucibles,  14. 

Gooch,  57,  58. 

Desiccators,  5. 

Desk,  equipment,  202. 

reagents,  concentration  of,  196. 
Dextrin,  determination  of,  125. 
Dextrose,  determination  of,  124, 

tables  for  207,  209. 
Diastase  method  for  starch,  126. 


Empirical  formula,  162. 
End  point,  52. 

Factor  weights,  calculation  of,  189. 

Factors,  165. 

Fat,  in  milk,  88,  92. 

in  butter,  composition  of,  103. 
Fatty   acids,  determination   of,    no,  112, 

"3- 

Feeding  materials,  analysis  of,  119,  122. 
Fertilizers,  analysis  of,  130. 
Filtration,  12. 

by  means  of  suction,  37. 

Gravimetric  analysis,  22. 
calculations  for,  163. 

Humus,  154. 

Hydrogen  peroxide,  purity  of,  73,  84. 

Indicators,  32. 

Indirect  methods,  calculation  for,  167. 

lodimetry,  78. 

calculations  for,  187. 
Iodine  absorption  number,  determination 

of,  1 1 6. 
Iron,  determination  of,  74,  77,  150,  153. 

Jones  reductor,  70. 

Kjeldahl  method  for  nitrogen,  94,  129,  138. 

Lactometers,  87. 

Lactose,  by  Soxhlet's  method,  table  for,  206. 

Logarithms,  table  of,  210-211. 

Magnesium,  determination  of,  33,  152. 
Manganese,  determination  of,  151. 
Milk,  analysis  of,  85. 


Nitrogen,  determination  of,  138,  155. 
Normal  solutions,  49,  50. 


217 


218 


INDEX 


Normality  factor,  59. 
Notebooks,  2,  53. 

Oleomargarine,  105,  115,  118. 
Operations  of  quantitative  analysis,  6-14. 
Oxalates,  determination  of  purity  of,  72. 
Oxidation  and  reduction,  calculations  for, 

178-185. 
Oxidation  processes,  64. 

Percentage  composition,  calculation  of,  162. 
Phosphorus,   determination  of,    132,   136, 

15°,  151- 

Platinum,  care  of,  15. 
Potassium,  determination  of,  140,  153. 
Precipitates,  colloidal,  12. 
crystalline,  n. 
drying  and  ignition  of,  14. 
Precipitation,  10. 
Problems,    162,  163,  166,    168,  171,    177, 

1 86,  1 88,  190. 
Proteids,  94,  129. 

Pyrolusite,  determination  of  available  oxy- 
gen in,  83. 

Questions  on  equations,  183,  188. 

Reagents,  4. 

laboratory,  table  of,  196-201. 

Saliva  method  for  starch,  127. 
Sampling,  6,  86,  101,  121,  131,  145. 
Saponification  numbers,  114. 
Siderite,  determination  of  iron  in,  74,  77. 


Silica,  148. 

Sodium,  determination  of,  153. 

Soil,  analysis  of,  142. 

constituents  of,  142,  145. 
Solutions,  normal,  49. 

preparation  for  iodimetry,  79. 

for  oxidation  and  reduction,  67,  79. 

standard,  49. 
Specific  gravity,  170. 

of  butter  fat,  106. 
Standardization  of  solutions, 

acid,  57,  62. 

alkali,  59. 

iodine,  80. 

methods  of,  54. 

potassium  dichromate,  76. 

potassium  permanganate,  68. 
Starch,  125,  127. 
Stirring  rods,  6. 
Stoichiometry,  161. 

Stone's  method  for  carbohydrates,  123. 
Sucrose,  124. 
Sulphur,  determination  of,  29,  152. 

Titration,  52. 

of  acid  against  the  alkali,  56. 

Volumetric  analysis,  40. 
apparatus,  40,  41. 

calibration  of,  42. 
calculations,  171. 

Wash  bottles,  6. 

Washing  of  precipitates,  13. 

Weighing,  precautions  in,  20. 


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BAILEY.  A  Text-Book  of  Sanitary  and  Applied  Chemistry;  or,  The  Chemistry  of 
Water,  Air,  and  Food.  By  E.  H.  S.  BAILEY,  Ph.D.,  Professor  of  Chemistry,  Uni- 
versity of  Kansas. 

20  +  J45  pages,  I2mo,  cl.,  $1,40  net 

BEEBE  AND  BUXTON.  Outlines  of  Physiological  Chemistry.  By  S.  P.  BEEBE, 
Ph.D.,  Physiological  Chemist  to  the  Huntington  Fund  for  Cancer  Research,  and 
B.  H.  BUXTON,  M.D.,  Professor  of  Experimental  Pathology,  Cornell  Medical  College. 

195  pages,  I2mo,  cl,,  $1.50  net 

BEHRENS.  A  Manual  of  Microchemical  Analysis.  By  Professor  H.  BEHRENS,  of 
the  Polytechnic  School  in  Delft,  Holland.  With  an  Introductory  Chapter  by  Pro- 
fessor John  W.  Judd,  F.R.S.,  of  the  Royal  College  of  Science.  With  84  Illustrations, 
drawn  by  the  Author. 

ii  +  246  pages,  i2mo,  cl.,  $1.50  net  {postage  <5V.) 

BLOUNT.  Practical  Electro-Chemistry.  By  BERTRAM  BLOUNT,  F.I.C.,  F.C.S.,  Assoc. 
Inst.  C.E.,  Consulting  Chemist  to  the  Crown  Agents  for  the  Colonies.  Second 
Impression. 

11  +  373  Pa8es>  c 

COHNHEIM.  Chemistry  of  the  Proteids.  By  Dr.  COHNHEIM.  Prepared  from  the 
Second  German  Edition  by  Dr.  Gustav  Mann,  Author  of  "  Physiological  Histology." 

8  +  600  pages,  8vo,  $3.73  net 

COMEY.  A  Dictionary  of  Chemical  Solubilities,  Inorganic.  By  ARTHUR  MESSINGER 
COMEY,  Ph.D.,  formerly  Professor  of  Chemistry,  Tufts  College. 

20  +  5*5  page* >  8vo,  cL,  $5.00  net 

FLEISCHER.  A  System  of  Volumetric  Analysis.  By  Dr.  EMIL  FLEISCHER.  Trans- 
lated, with  Notes  and  Additions,  from  the  Second  German  Edition,  by  M.  M.  Pattison 
Muir,  F.R.S.E.,  Assistant  Lecturer  on  Chemistry,  The  Owens  College,  Manchester. 

79  +  274  pages,  i2mo,  il.,  cl.,  $2.00  net 

GATTERMANN.  The  Practical  Methods  of  Organic  Chemistry.  By  LUDWIG  GAT- 
TERMANN,  Ph.D.,  Professor  in  the  University  of  Freiburg.  Authorized  Translation 
by  William  B.  Schober,  Ph.D.,  Instructor  in  Lehigh  University.  Second  American 
from  Fourth  German  Edition. 

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1 


STANDARD  BOOKS  ON  CHEMISTRY  —  Continued 


HEMPEL.  Methods  of  Gas  Analysis.  By  Dr.  WALTHER  HEMPEL,  Professor  of  Chem- 
istry in  Dresden  Technische  Hochschule.  Translated  from  the  Third  German 
Edition  and  Considerably  Enlarged  by  L.  M.  Dennis,  Professor  of  Analytical  and 
Inorganic  Chemistry  in  Cornell  University.  New  Edition. 

79  +  490  pages,  ismo,  il.,  cl.,  $2.25  net 

HERTER.  The  Common  Bacterial  Infections  of  the  Digestive  Tract,  and  the 
Intoxications  Arising  from  Them.  By  C.  A.  HERTER,  M.D.,  Professor  of  Phar- 
macology and  Therapeutics  in  Columbia  University,  Consulting  Physician  to  the 
City  Hospital,  New  York. 

x  +  360  pages,  index,  8vo,  cl.,  $/.jo  net;  by  mail,  $1.62  net 


HILLYER.  Laboratory  Manual  :  Experiments  to  Illustrate  the  Elementary  Principles 
of  Chemistry.  By  H.  W.  HILLYER,  Ph.D.,  Assistant  Professor  of  Organic  Chemistry 
in  the  University  of  Wisconsin. 

6  +  198  pages,  8vo,  cl.,  go  cents  net 

JONES.    The  Theory  of  Electrolytic  Dissociation  and  Some  of  its  Applications. 

12  +  289  pages,  i2tno,  cL,  $1.60  net 

Elements  of  Physical  Chemistry. 

ii  +  565  pages,  8vo,  cl.,  $4.00  net 

Elements  of  Inorganic  Chemistry. 


Principles  of  Inorganic  Chemistry. 

20  +  321  pages,  $3.00  net 

All  by  HARRY  C.  JONES,  Professor  of  Physical  Chemistry  in  the  Johns  Hopkins 
University,  Baltimore. 

LASSAR-COHN.  A  Laboratory  Manual  of  Organic  Chemistry.  A  Compendium  of 
Laboratory  Methods  for  the  Use  of  Chemists,  Physicians,  and  Pharmacists.  By  Dr. 
LASSAR-COHN.  Translated  from  the  Second  German  Edition  by  Alexander  Smith, 

B.Sc.,  Ph.D. 

79  +  203  pages,  8vo,  cl.,  $2.25  net 

LEBLANC.  The  Elements  of  Electro-Chemistry.  By  MAX  LEBLANC,  Professor  of 
Chemistry  in  the  University  of  Leipzig.  Translated  by  W.  R.  Whitney,  Instructor 
of  Chemistry  in  the  Massachusetts  Institute  of  Technology,  Boston.  New  Edition, 

revised  from  the  Third  German  Edition. 

10  +  282  pages,  i2ino,  cl.,  $1.50  net 

LENGFELD.  Inorganic  Chemical  Preparations.  By  FELIX  LENGFELD,  formerly 
Assistant  Professor  of  Inorganic  Chemistry  in  the  University  of  Chicago. 

9+55  pages*  i^mo,  cl.,  do  cents  net 


LEWKOWITSCH.    Chemical  Technology  and  Analysis  of  Oils,  Fats,  and  Waxes. 
Third  Edition.     Entirely  Rewritten  and  Enlarged.     Eighty-eight  Illustrations  and 

Numerous  Tables.     Two  Volumes. 

J0  _f.  I2  4.  Ifj2  pages,  8vo,  iL,  cl.,  $12.00  net 

LEWKOWITSCH.    Laboratory  Companion  to  Fats  and  Oils  Industries.    By  Dr. 
J.  LEWKOWITSCH,  M.A.,  F.I.C.,  Examiner  in  Soap  Manufacture  and  in  Fats  and 

Oils  to  the  City  and  Guild  of  London  Institute. 

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STANDARD  BOOKS  ON  CHEMISTRY  —  Continued 


LIVERSIDGE.  Tables  for  Qualitative  Chemical  Analysis.  Arranged  for  the  Use 
of  Students  by  A.  LIVERSIDGE,  M.A.,  LL.D.,  F.R.S.,  Professor  of  Chemistry  in  the 

University  of  Sydney.     Second  Edition. 

126  pages,  8vo,  cl.,  $1.30  net 

LUPTON.     Chemical  Arithmetic.     With  Twelve  Hundred  Examples.     By  SYDNEY 

LUPTON,  F.C.S. 

12  +  17 1  pages,  ibmo,  cl.,  -$1.10  net 

MENSCHUTKIN.  Analytical  Chemistry.  By  N.  MENSCHUTKIN,  Professor  in  the 
University  of  St.  Petersburg.  Translated  from  the  Third  German  Edition,  under 
the  Supervision  of  the  Author,  by  James  Locke. 

12  -\-  512  pages,  8vo,  cl.,  $4.00  net 

MEYER.  History  of  Chemistry  from  the  Earliest  Times  to  the  Present  Day.  By 
ERNEST  VON  MEYER,  Ph.D.  Translated  by  George  MacGowan,  Ph.D. 

8vo,  cl.,  $4.50  net 

MILLER.  The  Calculations  of  Analytical  Chemistry.  By  EDMUND  H.  MILLER, 
Ph.D.,  Professor  of  Analytical  Chemistry  in  Columbia  University.  Third  Edition. 

Revised  and  Enlarged. 

10  +  20 1  pages,  8vp,  cl.,  $1.50  net 

MORGAN.  Qualitative  Analysis  as  a  Laboratory  Basis  for  the  Study  of  General 
Inorganic  Chemistry.  By  WILLIAM  CONGER  MORGAN,  Ph.D.  (Yale),  Assistant 
Professor  of  Chemistry  in  the  University  of  California,  (c.) 

14  +  j/5  pages,  8vo,  il.,  cL,  $1.90  net 

NERNST.  Theoretical  Chemistry  from  the  Standpoint  of  Avogadro's  Rule  and 
Thermodynamics.  By  Professor  WALTER  NERNST,  Ph.D.,  of  the  University  of 
Gottingen.  Revised  by  the  Fourth  German  Edition. 

24  +  777  pages,  8vo,  cl.,  $3.75  net 

NOYES.  Qualitative  Chemical  Analysis,  with  Explanatory  Notes.  By  ARTHUR  A. 
NOYES,  Ph.D.,  Professor  of  Theoretical  Chemistry  in  the  Massachusetts  Institute  of 
Technology.  Third  Revised  and  Enlarged  Edition. 

89  pages,  8vo,  cL,  $1.25  net 

OSTWALD.  The  Scientific  Foundations  of  Analytical  Chemistry  Treated  in  an 
Elementary  Manner.  Translated  by  George  MacGowan,  Ph.D. 

31  +  799  pages,  8vo,  cl.,  $2.00  net 

Manual  of  Physico-Chemical  Measurements.     Translated  by  James   Walker, 
D.Sc.,  Ph.D. 

12  -f  253  pages,  il.,  cl.,  $2.25  net 

The  Principles  of  Inorganic  Chemistry.    Translated  with  the  Author's  Sanction 
by  Alexander  Findlay,  M.A.,  B.Sc.,  Ph.D.     With  122  Figures  in  the  Text. 

27  +  785  pages,  8vo,  cl.,  $6.00  net 

All  by  WILHELM  OSTWALD,  Professor  of  Chemistry  in  the  University  of  Leipzig. 

REYCHLER.  Outlines  of  Physical  Chemistry.  By  A.  REYCHLER,  Professor  of 
Chemistry  in  the  University  of  Brussels.  Authorized  Translation  by  John  McCrae, 
Ph.D.  (Heid.).  With  52  Illustrations.  Second  Edition. 

16  +  268  pages,  cl.,  $1.00  net 
3 


STANDARD  BOOKS  ON  CHEMISTRY  -  Continued 


ROLFE.  The  Polariscope  in  the  Chemical  Laboratory.  An  Introduction  to  Polar- 
imetry  and  its  Application.  By  GEORGE  WILLIAM  ROLFE,  A.M.,  Instructor  in 
Sugar  Analysis  in  the  Massachusetts  Institute  of  Technology. 

7  +  320 pages,  i2mo,  il.,  cl.,  $1.90  net. 

ROSCOE  AND  SCHORLEMMER.  A  Treatise  on  Chemistry.  By  Sir  HENRY  E. 
ROSCOE  and  C.  SCHORLEMMER,  F.R.S.  Vol.  I  —  The  Non-Metallic  Elements.  New 
Edition.  Completely  Revised  by  Sir  H.  Roscoe,  Assisted  by  Drs.  Colman  and 
Harden. 

12  +  931  pages,  8vo,  cl.,  $5.00  net 

SCHNABEL.  Handbook  of  Metallurgy.  By  Dr.  CARL  SCHNABEL,  Konigl.  Preuss. 
Bergrath  Professor  of  Metallurgy.  Translated  by  Henry  Louis,  M.A.,  A.R.S.M., 
F.I.C.,  etc.,  Professor  of  Mining  at  Armstrong  College,  Newcastle-upon-Tyne. 
Second  Edition.  Vol.  I  — Copper,  Lead,  Silver,  Gold.  Illustrated  with  715 
Figures,  (c.) 

20  +  1123  pages,  8vo,  il.,  cl.,  $6.50  net 

SCHULTZ  AND  JULIUS.  A  Systematic  Survey  of  the  Organic  Colouring  Matters. 
Founded  on  the  German  of  Drs.  G.  SCHULTZ  and  P.  JULIUS.  Second  Edition.  Re- 
vised Throughout  and  Greatly  Enlarged  by  Arthur  G.  Green,  F.I.C.,  F.C.S. 

10  +  280  pages,  imperial  8vo,  cl.,  -$7.00  net 

SHERMAN.  Methods  of  Organic  Analysis.  By  HENRY  C.  SHERMAN,  Ph.D.,  Adjunct 
Professor  of  Analytical  Chemistry  in  Columbia  University. 

2 45  pages,  8vo,  cl.,  $1.75  net  {postage  /^.) 

TALBOT.  An  Introductory  Course  of  Quantitative  Chemical  Analysis,  with  Ex- 
planatory Notes  and  Stoichiometrical  Problems.  By  HENRY  P.  TALBOT,  Ph.D., 
Professor  of  Inorganic  and  Analytical  Chemistry  in  the  Massachusetts  Institute  of 
Technology. 

153  pages,  8vo,  cl.,  $1.50  net 

TALBOT  AND  BLANCHARD.  The  Electrolytic  Dissociation  Theory.  With  Some 
of  its  Applications.  An  Elementary  Treatise  for  the  Use  of  Students  in  Chemistry. 
By  Professor  H.  P.  TALBOT  and  ARTHUR  A.  BLANCHARD,  both  of  the  Massachusetts 
Institute  of  Technology. 

4  +  84  pages,  8vo,  cl.,  $1.25  net 

THORP.  Outlines  of  Industrial  Chemistry :  A  Text-Book  for  Students.  By  FRANK 
HALL  THORP,  Ph.D.,  Assistant  Professor  of  Industrial  Chemistry  in  the  Massachu- 
setts Institute  of  Technology.  Second  Edition.  Revised  and  Enlarged,  and  Includ- 
ing a  Chapter  on  Metallurgy  by  Charles  D.  Demond,  S.B.,  Testing  Engineer  of  the 
Anaconda  Mining  Company. 

26  +  618  pages,  8vo,  il.,  cl.,  $3.75  net 

WALKER.  Introduction  to  Physical  Chemistry.  By  JAMES  WALKER,  D.Sc.,  Ph.D., 
F.R.S.,  Professor  of  Chemistry  in  University  College,  Dundee.  Fourth  Edition. 

12  +  387  pages,  8vo,  cl.,  $3.25  net 

YOUNG.  Fractional  Distillation.  By  SYDNEY  YOUNG,  D.Sc.,  F.R.S.  With  72 
Illustrations. 

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